Solid-state multinuclear magnetic resonance and X-ray crystallographic investigation of the phosphorus...iodine halogen bond in a bis(dicyclohexylphenylphosphine)(1,6-diiodoperfluorohexane) cocrystal.

Halogen bonding to phosphorus atoms remains uncommon, with relatively few examples reported in the literature. Here, the preparation and investigation of the cocrystal bis(dicyclohexylphenylphosphine)(1,6-diiodoperfluorohexane) by X-ray crystallography and solid-state multinuclear magnetic resonance spectroscopy is described. The crystal structure features two crystallographically unique C-I...P halogen bonds [dI...P = 3.090 (5) Å, 3.264 (5) Å] and crystallographic disorder of one of the 1,6-diiodoperfluorohexane molecules. The first of these is the shortest and most linear I...P halogen bond reported to date. 13C, 19F, and 31P magic angle spinning solid-state NMR spectra are reported. A 31P chemical shift change of -7.0 p.p.m. in the cocrystal relative to pure dicyclohexylphenylphosphine, consistent with halogen bond formation, is noted. This work establishes iodoperfluoroalkanes as viable halogen bond donors when paired with phosphorus acceptors, and also shows that dicyclohexylphenylphosphine can act as a practical halogen bond acceptor.

[Design Strategy of Biologically Active Compounds Using Various Elements].

Almost all conventional drug discovery research has been based on hydrocarbon-based frameworks and common chemical elements such as nitrogen, oxygen, sulfur, and the halogens. However, triggered by the approval of bortezomib, a boronic acid-containing pharmaceutical agent, the incorporation of functionalities that are not native in biological systems has been intensively investigated. Several other boron-containing pharmaceuticals have also been marketed. Therefore, the inclusion of various elements is one of the most promising strategies for the development of novel and distinctive drug candidates. In this symposium review, the author focused on the 'elements chemistry' approaches for the structural development of biologically active compounds, particularly those involving silicon and phosphorus. The isosteric exchange of Si and C (Si/C-exchange) is one of the most-investigated forms of substituting elements. We revealed the detailed physicochemical impact of Si/C-exchange, and we proposed several applications of silyl functionalities other than the simple Si/C-exchange. Regarding phosphorus, we recently revealed that the P-B substructure can function as the isostere of C-C or Si-C substructures. In addition to these isosteric exchanges, the development of biologically active compounds bearing unique substructures such as carboranes, hydrophobic boron clusters, and ferrocene is introduced. These novel strategies provide several options for structural development, offering great potential for expanding the chemical space of medicinal chemistry.

Preservation of Aloe vera and soybean flour fortified Granny Smith apple through optimised quartz-halogen radiated vacuum drying: kinetics and quality evaluation.

BACKGROUND: Granny Smith (GS) apple has low protein content and poor antimicrobial properties; hence it has been blended with Aloe vera (AV; high ascorbic acid, antimicrobial and antioxidant properties) and soybean flour (SF; rich in phenols, flavonoids, ascorbic acid, total antioxidant and protein) in different proportions to obtain fortified GS, i.e. GSAVSF. Moreover, GS being a perishable fruit, its moisture content should be reduced to enhance shelf life. Accordingly, this GSAVSF was osmotically pre-dehydrated and finally dried through energy-efficient quartz-halogen radiation (QHR) assisted vacuum-drying (QHRVD) to produce dried GSAVSF i.e. (DGSAVSF) under optimized conditions. RESULTS: The optimally dehydrated DGSAVSF product resulted in minimum moisture (4.85% w/w) and maximum protein (6.24 g kg-1 ) content. The application of osmotic dehydration and QHRVD afforded acceptable colour of DGSAVSF compared to GSAVSF (ΔEI * = 10.07 ± 0.21). A parametric drying model was formulated that corroborated well with Fick's equation. QHRVD rendered high moisture diffusivity (1.49 × 10-8 m2 s-1 ) and low activation energy (27.64 kJ mol-1  K-1 ). Appreciable quality improvements with respect to fresh GS concerning ascorbic acid (176.05%), total phenolic (579.07%), total flavonoid (333.33%) contents and 2,2'-diphenyl-1-picrylhydrazyl radical scavenging activity (446.71%) could be achieved. The product demonstrated satisfactory shelf life (1 × 104 CFU g-1 : aerobic mesophilic; 1 × 104 CFU g-1 : mould and yeast) and high rehydration ratio (4.25 ± 0.1). CONCLUSION: The enrichment of GS with AV and SF along with optimal drying protocols could provide a quality fortified DGSAVSF through an energy-proficient sustainable process. The highly nutritious product with suitable colour, microbial stability and rehydration ratio also satisfied a 9-point hedonic scale, thus confirming consumer acceptability. © 2020 Society of Chemical Industry.

Thyroxine binding to type III iodothyronine deiodinase.

Iodothyronine deiodinases (Dios) are important selenoproteins that control the concentration of the active thyroid hormone (TH) triiodothyronine through regioselective deiodination. The X-ray structure of a truncated monomer of Type III Dio (Dio3), which deiodinates TH inner rings through a selenocysteine (Sec) residue, revealed a thioredoxin-fold catalytic domain supplemented with an unstructured Ω-loop. Loop dynamics are driven by interactions of the conserved Trp207 with solvent in multi-microsecond molecular dynamics simulations of the Dio3 thioredoxin(Trx)-fold domain. Hydrogen bonding interactions of Glu200 with residues conserved across the Dio family anchor the loop's N-terminus to the active site Ser-Cys-Thr-Sec sequence. A key long-lived loop conformation coincides with the opening of a cryptic pocket that accommodates thyroxine (T4) through an I⋯Se halogen bond to Sec170 and the amino acid group with a polar cleft. The Dio3-T4 complex is stabilized by an I⋯O halogen bond between an outer ring iodine and Asp211, consistent with Dio3 selectivity for inner ring deiodination. Non-conservation of residues, such as Asp211, in other Dio types in the flexible portion of the loop sequence suggests a mechanism for regioselectivity through Dio type-specific loop conformations. Cys168 is proposed to attack the selenenyl iodide intermediate to regenerate Dio3 based upon structural comparison with related Trx-fold proteins.

In situ biogenic synthesis of Pd nanoparticles over reduced graphene oxide by using a plant extract (Thymbra spicata) and its catalytic evaluation towards cyanation of aryl halides.

An eco-friendly biosynthesized Pd NP anchored Thymbra spicata extract-modified graphene oxide (Pd NPs/rGO-T. spicata) nanohybrid material has been introduced. Initially, the herb, Thymbra spicata extract was immobilized on the surface of GO via their natural adhering capability. The polyphenolic function grafted in situ prepared RGO acted as the natural reductant of Pd precursor. The as-prepared nanocomposite (Pd NPs/rGO-T. spicata) was characterized using Fourier transform infrared (FTIR), UV-vis, X-ray diffraction (XRD), inductively coupled plasma (ICP), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), high resolution transmission electron microscopy (HRTEM), Fast Fourier Transform (FFT), Raman spectroscopy and EDX elemental mapping techniques. It has been observed that the Pd NPs with perfect crystal structure, uniform shape and size were dispersed homogeneously on the rGO surface. The material showed excellent water dispersibility due to the hydrophilicity of biomolecules attached over them, which is very essential in heterogeneous catalysis. The T. spicata contained biomolecules served as effective capping, reducing and stabilizing agents for the uniform immobilization of Pd precursors on graphene sheet surface without aggregation. The catalytic activity of this nano hybrid was assessed comprehensively in the cyanation of aryl halides with a wide range of substrates using K4[Fe(CN)6] as a cheap source of cyanide. The model reaction resulted outstanding catalytic performance with a great reusability of the catalysis.

The application of new HARD-descriptor available from the CORAL software to building up NOAEL models.

Continuous QSAR models have been developed and validated for the prediction of no-observed-adverse-effect (NOAEL) in rats, using training and test sets from the Fraunhofer RepDose® database and EFSA's Chemical Hazards Database: OpenFoodTox. This paper demonstrates that the HARD index, as an integrated attribute of SMILES, improves the prediction power of NOAEL values using the continuous QSAR models and Monte Carlo simulations. The HARD-index is a line of eleven symbols, which represents the presence, or absence of eight chemical elements (nitrogen, oxygen, sulfur, phosphorus, fluorine, chlorine, bromine, and iodine) and different kinds of chemical bonds (double bond, triple bond, and stereo chemical bond). Optimal molecular descriptors calculated with the Monte Carlo technique (maximization of correlation coefficient between the descriptor and endpoint) give satisfactory predictive models for NOAEL. Optimal molecular descriptors calculated in this way with the Monte Carlo technique (maximization of correlation coefficient between the descriptor and endpoint) give amongst the best results available in the literature. The models are built up in accordance with OECD principles.

Metabolite diversification by cultivation of the endophytic fungus Dothideomycete sp. in halogen containing media: Cultivation of terrestrial fungus in seawater.

The endophytic fungus, Dothideomycete sp. CRI7, isolated from the terrestrial plant, Tiliacora triandra, was salt tolerant, capable of growing in the culture medium prepared from seawater; salts in seawater did not have any effects on the fungal growth. Metabolite productions of the fungus CRI7 cultivated in media prepared from seawater (MSW), prepared from deionized water supplemented with potassium bromide (MKBr) or potassium iodide (MKI), and prepared from deionized water (MDW) were investigated. It was found that the cultivation of the fungus CRI7 in MKBr and MSW enabled the fungus to produce nine new metabolites (1-9). The production of an azaphilone, austdiol (10), of the fungus CRI7 grown in MDW was 0.04g/L, which was much lower than that grown in MSW, MKBr, and MKI media which provided the yields of 0.5, 0.9, and 1.2g/L, respectively, indicating that halogen salts significantly enhanced the production of the polyketide 10. The cultivation of terrestrial fungi in media containing halogen salts could therefore be useful for the metabolite diversification by one strain-many compounds (OSMAC) approach. Moreover, the isolated polyketides had significant biosynthetic relationship, suggesting that the cultivation of fungi in halogen containing media could provide the insights into certain polyketide biosynthesis. One of the isolated compounds exhibited antibacterial activity with the MIC value of 100µg/mL.

Identification of acylthiourea derivatives as potent Plk1 PBD inhibitors.

Thiourea derivatives have drawn much attention for their latent capacities of biological activities. In this study, we designed acylthiourea compounds as polo-like kinase 1 (Plk1) polo-box domain (PBD) inhibitors. A series of acylthiourea derivatives without pan assay interference structure (PAINS) were synthesized. Four compounds with halogen substituents exhibited binding affinities to Plk1 PBD in low micromole range. The most potent compound (3v) showed selectivity over other subtypes of Plk PBDs and inhibited the kinase activity of full-length Plk1.

Repositioning organohalogen drugs: a case study for identification of potent B-Raf V600E inhibitors via docking and bioassay.

Drug repositioning has been attracting increasingly attention for its advantages of reducing costs and risks. Statistics showed that around one quarter of the marketed drugs are organohalogens. However, no study has been reported, to the best of our knowledge, to aim at efficiently repositioning organohalogen drugs, which may be attributed to the lack of accurate halogen bonding scoring function. Here, we present a study to show that two organohalogen drugs were successfully repositioned as potent B-Raf V600E inhibitors via molecular docking with halogen bonding scoring function, namely D(3)DOCKxb developed in our lab, and bioassay. After virtual screening by D(3)DOCKxb against the database CMC (Comprehensive Medicinal Chemistry), 3 organohalogen drugs that were predicted to form strong halogen bonding with B-Raf V600E were purchased and tested with ELISA-based assay. In the end, 2 of them, rafoxanide and closantel, were identified as potent inhibitors with IC50 values of 0.07 µM and 1.90 µM, respectively, which are comparable to that of vemurafenib (IC50: 0.17 µM), a marketed drug targeting B-Raf V600E. Single point mutagenesis experiments confirmed the conformations predicted by D(3)DOCKxb. And comparison experiment revealed that halogen bonding scoring function is essential for repositioning those drugs with heavy halogen atoms in their molecular structures.

Synthesis and Th1-immunostimulatory activity of α-galactosylceramide analogues bearing a halogen-containing or selenium-containing acyl chain.

A novel series of CD1d ligand α-galactosylceramides (α-GalCers) were synthesized by incorporation of the heavy atoms Br and Se in the acyl chain backbone of α-galactosyl-N-cerotoylphytosphingosine. The synthetic analogues are potent CD1d ligands and stimulate mouse invariant natural killer T (iNKT) cells to selectively enhance Th1 cytokine production. These synthetic analogues would be efficient X-ray crystallographic probes to disclose precise atomic positions of alkyl carbons and lipid-protein interactions in KRN7000/CD1d complexes.

What Is Moving in Hybrid Halide Perovskite Solar Cells?

Organic-inorganic semiconductors, which adopt the perovskite crystal structure, have perturbed the landscape of contemporary photovoltaics research. High-efficiency solar cells can be produced with solution-processed active layers. The materials are earth abundant, and the simple processing required suggests that high-throughput and low-cost manufacture at scale should be possible. While these materials bear considerable similarity to traditional inorganic semiconductors, there are notable differences in their optoelectronic behavior. A key distinction of these materials is that they are physically soft, leading to considerable thermally activated motion. In this Account, we discuss the internal motion of methylammonium lead iodide (CH3NH3PbI3) and formamidinium lead iodide ([CH(NH2)2]PbI3), covering: (i) molecular rotation-libration in the cuboctahedral cavity; (ii) drift and diffusion of large electron and hole polarons; (iii) transport of charged ionic defects. These processes give rise to a range of properties that are unconventional for photovoltaic materials, including frequency-dependent permittivity, low electron-hole recombination rates, and current-voltage hysteresis. Multiscale simulations, drawing from electronic structure, ab initio molecular dynamic and Monte Carlo computational techniques, have been combined with neutron diffraction measurements, quasi-elastic neutron scattering, and ultrafast vibrational spectroscopy to qualify the nature and time scales of the motions. Electron and hole motion occurs on a femtosecond time scale. Molecular libration is a sub-picosecond process. Molecular rotations occur with a time constant of several picoseconds depending on the cation. Recent experimental evidence and theoretical models for simultaneous electron and ion transport in these materials has been presented, suggesting they are mixed-mode conductors with similarities to fast-ion conducting metal oxide perovskites developed for battery and fuel cell applications. We expound on the implications of these effects for the photovoltaic action. The temporal behavior displayed by hybrid perovskites introduces a sensitivity in materials characterization to the time and length scale of the measurement, as well as the history of each sample. It also poses significant challenges for accurate materials modeling and device simulations. There are large differences between the average and local crystal structures, and the nature of charge transport is too complex to be described by common one-dimensional drift-diffusion models. Herein, we critically discuss the atomistic origin of the dynamic processes and the associated chemical disorder intrinsic to crystalline hybrid perovskite semiconductors.

A Halogen-Containing Stilbene Derivative from the Leaves of Cajanus cajan that Induces Osteogenic Differentiation of Human Mesenchymal Stem Cells.

A new natural halogen-containing stilbene derivative was isolated from the leaves of Cajanus cajan (L.) Millsp. and identified as 3-O-(3-chloro-2-hydroxyl-propanyl)-longistylin A by comprehensive spectroscopic and chemical analysis, and named cajanstilbene H (1). It is the first halogen-containing stilbene derivative found from plants. In human mesenchymal stem cells (hMSC) from bone marrow, 1 did not promote cell proliferation, but distinctly enhanced osteogenic differentiation of hMSC in time- and dose-dependent manners. In six human cancer cell lines, 1 showed a moderate inhibitory effect on cell proliferation, with IC50 values of 21.42-25.85 µmol·L(-1).

Se···N chalcogen bond and Se···X halogen bond involving F2C═Se: influence of hybridization, substitution, and cooperativity.

Quantum-chemical calculations have been performed for the chalcogen- and halogen-bonded complexes of F2CSe with a series of nitrogen bases (N2, NCH, NH3, NHCH2, NCLi, and NMe3) and dihalogen molecules (BrCl, ClF, and BrF), respectively. Both types of interactions are mainly driven by the electrostatic and orbital interactions. The chalcogen bond becomes stronger in the order of NCH (sp) < NH3 (sp(3)) < NHCH2 (sp(2)), showing some inconsistence with the electronegativity of the hybridized N atom. The Li and methyl groups have an enhancing effect on the strength of chalcogen bond; however, the former is jointly achieved through the electrostatic and orbital interactions, whereas the orbital interaction has dominant contribution to the latter enhancement. The halogen bond with F2CX (X = O, S, Se) as the electron donor is stronger for the heavier chalcogen atom, exhibiting a reverse dependence on the chalcogen atom with that in hydrogen bonds. The halogen bond is further strengthened by the presence of chalcogen bond in the ternary complexes. In addition, CSD research confirms the abundance of Se···N interaction in crystal materials.

Pnicogen and hydrogen bonds: complexes between PH3X(+) and PH2X systems.

The charge-assisted complexes between PH3X(+) and PH2X have been analyzed. MP2/aug'-cc-pVTZ calculations were performed and the results were supported by the Quantum Theory of Atoms in Molecules approach and the Natural Bond Orbitals method. It was found that three different configurations could be formed, i.e. those linked through a P···P or a P···X pnicogen bond and those linked through a P-H···P hydrogen bond. The P···P configurations are the most stable ones corresponding to the strongest interactions; for all complexes the P···P configuration exists, while the P···X and P-H···P ones are present only for some of them. Different relations between the parameters were found, especially for the P···P interactions where there are correlations between the P···P distance and the electron density at the P···P bond critical point (ρPP) as well as between ρPP and the charge transfer energy.

Substituent effects on the properties of pnicogen-bonded complexes H2XP:PYH2, for X, Y = F, Cl, OH, NC, CCH, CH3, CN, and H.

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out on the pnicogen-bonded homodimers (PH2X)2 and the binary complexes H2XP:PYH2, for X, Y = F, Cl, OH, NC, CCH, CH3, CN, and H. The binding energies of these complexes are influenced by the nature of the X,Y pair, the intermolecular distance, the relative orientation of the interacting molecules, and the charge-transfer energies from the lone pair of one P to the σ-hole of the other. Binary complexes with X,Y = F, Cl, OH, and NC, as well as the homodimers, have a trans arrangement of the P-A and P-A' bonds with respect to the P···P bond, with A and A', the atoms of X and Y, respectively, bonded to the P atoms. The trendlines for the homodimers in plots of the binding energy versus the P-P distance, and the binding energy versus the total charge-transfer energy, exhibit better correlations than the trendlines for the binary complexes. The trendlines for the homodimers mark the boundary of the region in which points for the binary complexes appear. Pnicogen-bond radii for P in PH2X molecules have been determined from the P-P distances in the homodimers. The sum of these radii provides an excellent approximation to the P-P distance in the corresponding binary complex. EOM-CCSD spin-spin coupling constants (1p)J(P-P) have also been computed for all complexes. Coupling constants for the dimers and binary complexes exhibit a similar linear increase as the P-P distance decreases.

1,3-Halogen migration as an entry to aryl coppers from an unintuitive starting material.

A copper(I) catalyzed 1,3-halogen migration/borylation migrates a bromine from an sp(2) carbon to a benzylic carbon with concomitant borylation of the aryl-bromine bond. This transformation proceeds via an aryl copper intermediate which can be accessed independently and then trapped with electrophiles. As such, copper-catalyzed 1,3-halogen migration provides unique and mild access to an aryl copper species that allows for rapid aromatic functionalization from an unconventional starting material.

Redox properties of biscyclopentadienyl uranium(V) imido-halide complexes: a relativistic DFT study.

Calculations of ionization energies (IE) and electron affinities (EA) of a series of biscyclopentadienyl imido-halide uranium(V) complexes Cp*2U(=N-2,6-(i)Pr2-C6H3)(X) with X = F, Cl, Br, and I, related to the U(IV)/U(V) and U(V)/U(VI) redox systems, were carried out, for the first time, using density functional theory (DFT) in the framework of the relativistic zeroth order regular approximation (ZORA) coupled with the conductor-like screening model (COSMO) solvation approach. A very good linear correlation (R(2) = 0.993) was obtained, between calculated ionization energies at the ZORA/BP86/TZP level, and the experimental half-wave oxidation potentials E1/2. A similar linear correlation between the computed electron affinities and the electrochemical reduction U(IV)/U(III) potentials (R(2) = 0.996) is obtained. The importance of solvent effects and of spin-orbit coupling is definitively confirmed. The molecular orbital analysis underlines the crucial role played by the 5f orbitals of the central metal whereas the Nalewajski-Mrozek (N-M) bond indices explain well the bond distances variations following the redox processes. The IE variation of the complexes, i.e., IE(F) < IE(Cl) < IE(Br) < IE(I) is also well rationalized considering the frontier MO diagrams of these species. Finally, this work confirms the relevance of the Hirshfeld charges analysis which bring to light an excellent linear correlation (R(2) = 0.999) between the variations of the uranium charges and E1/2 in the reduction process of the U(V) species.

Pnicogen-bonded anionic complexes.

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to investigate the pnicogen-bonded complexes H2YP:X(-), for X,Y = Cl, NC, F, CCH, and CH3. Of the 36 possible complexes, only 21 are unique equilibrium structures. All substituents form (H2XPX)(-) complexes with symmetric X-P-X bonds. The P-A ion-molecule pnicogen bonds in these and some additional complexes have partial covalent character, while some P-A' covalent bonds have partial ion-molecule character. A and A' are the atoms of X and Y, respectively, which are directly bonded to P. Complexes with these types of bonds include the symmetric complexes (H2XPX)(-), H2(CH3)P:F(-), H2(CCH)P:F(-), H2FP:NC(-), H2FP:Cl(-), H2FP:CN(-), and H2(NC)P:Cl(-). Charge transfer from A to the P-A' σ* orbital stabilizes H2YP:X(-) complexes and leads to a reduction of the negative charge on X. For fixed X, the smallest negative charge occurs in the symmetric complex. Then, for a given X, the order of decreasing negative charge with respect to Y is CH3 > CCH > CN (bonded through C) > F > NC (bonded through N) > Cl, which is also the order of decreasing P-A distance. EOM-CCSD spin-spin coupling constants (1p)J(P-A) differentiate between shorter ion-molecule pnicogen bonds with partial covalent character and longer P···A ion-molecule pnicogen bonds. Similarly, coupling constants (1)J(P-A') differentiate between longer covalent P-A' bonds with partial ion-molecule character and shorter P-A' covalent bonds.

Influence of substituent effects on the formation of P···Cl pnicogen bonds or halogen bonds.

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out in search of equilibrium structures with P···Cl pnicogen bonds or halogen bonds on the potential energy surfaces H2FP:ClY for Y = F, NC, Cl, CN, CCH, CH3, and H. Three different types of halogen-bonded complexes with traditional, chlorine-shared, and ion-pair bonds have been identified. Two different pnicogen-bonded complexes have also been found on these surfaces. The most electronegative substituents F and NC form only halogen-bonded complexes, while the most electropositive substituents CH3 and H form only pnicogen-bonded complexes. The halogen-bonded complexes involving the less electronegative groups Cl and CN are more stable than the corresponding pnicogen-bonded complexes, while the pnicogen-bonded complexes with CCH are more stable than the corresponding halogen-bonded complex. Traditional halogen-bonded complexes are stabilized by charge transfer from the P lone pair to the Cl-A σ* orbital, where A is the atom of Y directly bonded to Cl. Charge transfer from the Cl lone pair to the P-F σ* orbital stabilizes pnicogen-bonded complexes. As a result, the H2FP unit becomes positively charged in halogen-bonded complexes and negatively charged in pnicogen-bonded complexes. Spin-spin coupling constants (1X)J(P-Cl) for complexes with traditional halogen bonds increase with decreasing P-Cl distance, reach a maximum value for complexes with chlorine-shared halogen bonds, and then decrease and change sign when the bond is an ion-pair bond. (1p)J(P-Cl) coupling constants across pnicogen bonds tend to increase with decreasing P-Cl distance.

Pnicogen bonds between X═PH3 (X = O, S, NH, CH2) and phosphorus and nitrogen bases.

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to investigate the pnicogen bonded complexes formed between the acids O═PH3, S═PH3, HN═PH3, and H2C═PH3 and the bases NH3, NCH, N2, PH3, and PCH. All nitrogen and phosphorus bases form complexes in which the bases are lone pair electron donors. The binding energies of complexes involving the stronger bases NH3, NCH, and PH3 differentiate among the acids, but the binding energies of complexes with the weaker bases do not. These complexes are stabilized by charge transfer from the lone pair orbital of N or P to the σ*P═A orbital of X═PH3, where A is the atom of X directly bonded to P. PCH also forms complexes with the X═PH3 acids as a π electron donor to the σ*P═A orbital. The binding energies and the charge-transfer energies of the π complexes are greater than those of the complexes in which PCH is a lone pair donor. Whether the positive charge on P increases, decreases, or remains the same upon complex formation, the chemical shieldings of (31)P decrease in the complexes relative to the corresponding monomers. (1p)J(P-N) and (1p)J(P-P) values correlate best with the corresponding P-N and P-P distances as a function of the nature of the base. (1)J(P-A) values do not correlate with P-A distances. Rather, the absolute values of (1)J(P-O), (1)J(P-S), and (1)J(P-N) decrease upon complexation. Decreasing (1)J(P-A) values correlate linearly with increasing complex binding energies. In contrast, (1)J(P-C) values increase upon complexation and correlate linearly with increasing binding energies.