BACKGROUND: THE “TERM HALOGEN BOND” (XB) IS USED TO DESCRIBE ANY NONCOVALENTINTERACTION INVOLVING HALOGEN AS ACCEPTOR OF ELECTRON DENSITY [1]. XB IS A CONSEQUENCE OF INTERACTION BETWEEN Y AND THE Ζ-HOLE REGION OF X AND IS BELIEVED TO BE MAINLY OF THE ELECTROSTATICNATURE [2]. HEREIN, CHARACTERIZATION OF HALOGEN BONDS WERE PERFORMED USING THE TOPOLOGICAL PROPERTIES OFELECTRON DENSITY OBTAINED FROM ATOMS IN MOLECULES (AIM) ANALYSIS OF BIS (PYRIDINE) HALONIUM. (SEE FIGURE 1)METHODS: ALL STRUCTURES WERE OPTIMIZED USING GAUSSIAN 09 PROGRAM PACKAGE AT THE B3LYP/6-311++G** LEVEL. THE LANL2DZ BASIS SETS WAS EMPLOYED FORIODINE. THE TOPOLOGICAL ANALYSIS OFELECTRON DENSITY WERE COMPUTED BY THEAIM2000 PROGRAM.RESULTS: THE VALUES OF ELECTRON DENSITY RB, LAPLACIAN OF ELECTRON DENSITY D2RB, ELECTRON ENERGY DENSITY HB AND -GB/VB, WHICH IS THE RATIO OF THE KINETIC ENERGY DENSITY TO THE POTENTIAL ENERGY DENSITY AT THE BCP, ARE IN THE RANGES ILLUSTRATED IN THE TABLE 1, WITH THE SHARED-SHELL AND CLOSED-SHELL AS TWO LIMITED INTERACTIONS.

THE QUANTUM THEORY OF ATOMS IN MOLECULES (qtaim) IS ONE OF THE MOST POWERFUL TOOLS WHICH ALLOW DEEPEN THE NATURE OF INTRAMOLECULAR HYDROGEN BONDING (IHB) INTERACTIONS. IN THIS STUDY THE qtaim APPROACH IS APPLIED TO INVESTIGATE THE NATURE OF O-H···O BONDS OF 1, 5-DIHYDROXYANTHRAQINONE (1, 5DHA), AND COMPARE TO THE ANALOGOUS PARAMETERS OF 2-HYDROXYBENZALDEHYDE (2HB) AND 1-HYDROXYANTHRACEN -9 (10H) -ONE (1HA)...

THE LAST THREE DECADES WITNESS AN UNPRECEDENTED PROGRESS IN THE FIELD OF COMPUTATIONAL AB INITIO QUANTUM CHEMISTRY AND BECAUSE OF THESE ADVANCES NOWADAYS RELIABLE AB INITIO COMPUTATIONS ON LARGE SCALE MOLECULES ARE QUITE FEASIBLE. SUCH STATE-OF-ART AB INITIO PROCEDURES USUALLY YIELD INTRICATE WAVE FUNCTIONS CONTAINING A WEALTH OF CHEMICAL INFORMATION THAT ARE HARD TO EXTRACT BASED ON TRADITIONAL "PAPER AND PENCIL" METHODS..

INTRODUCTION: WHEN TWO LEWIS BASE (A AND B) COMPETE FOR THE SAME PROTON THE RESULT IS A STRONG BINARY COMPLEX, [A···H+···B], WHICH CAN PLAY AN IMPORTANT ROLE IN BIOLOGICAL AND PHYSICAL PROCESSES REQUIRING PROTON TRANSPORT. THUS PROTON BONDS ARE BELIEVED TO BE MAINLY OF THE ELECTROSTATIC NATURE...

IN ORDER TO EXPLORE THE HYDROGEN BINDING INTERACTIONS BETWEEN PARACETAMOL (ACETAMINOPHEN) AND WATER MOLECULES, WE HAVE CALCULATED THE GEOMETRIC STRUCTURES AS WELL AS THE TOTAL ENERGIES OF THE VARIOUS HYDROGEN-BONDED PARACETAMOL-WATER COMPLEXES COMPOSED BASED ON THE ATOMIC CHARGES OBTAINED FROM THE NBO ANALYSIS [1, 2]. IT WAS FOUND THAT THERE ARE THREE SITES (O11, N13, O20) WITHIN THE PARACETAMOL MOLECULE THROUGH WHICH INTERMOLECULAR HYDROGEN BONDS CAN BE FORMED WITH WATER MOLECULE. ALL THE CALCULATIONS HAVE BEEN PERFORMED USING THE DENSITY FUNCTIONAL THEORY (DFT) METHOD WITH THE B3PW91 FUNCTIONAL AND 6-31+G (D, P) BASIS SET. FURTHERMORE, BY COMPARING THE HYDROGEN BOND LENGTHS AND THE RELATIVE ENERGIES OF THE THREE HYDROGEN-BONDED COMPLEXES PARACETAMOL-H2O, WE FOUND THAT HYDROGEN BONDS FORMED AT THE CARBONYL OXYGEN ATOM (O20) ARE STRONGER THAN THOSE FORMED AT HETEROATOM O11 AND N13. MOREOVER, AS THE NUMBER OF THE WATER MOLECULES HYDROGEN-BONDED TO THE PARACETAMOL INCREASES, THE HYDROGENBONDED COMPLEX PARACETAMOL-WATER BECOMES MORE STABLE. AT THE END, THE QUANTUM THEORY ATOMS IN MOLECULES (qtaim) THEORY [3, 4] WAS APPLIED TO EXPLAIN THE NATURE OF HETROATOM…HOH INTERACTIONS IN PARACETAMOL-WATER COMPLEXES. FROM THE RESULTS OF qtaim, IT IS EVIDENT THAT THE VALUES OF RBCP (CHARGE DENSITY OF CRITICAL POINT) ARE CALCULATED TO BE IN THE RANGE OF 0.011_0.480 AU, WHEREAS THE VALUES OF Ñ2RBCP FOR O20…H, N13…H AND O11…H ARE ALL POSITIVE, RANGING FROM 0.023 TO 0.092 AU. THESE VALUES WERE WITHIN THE COMMON ACCEPTED VALUES FOR H-BONDING INTERACTIONS, THUS INDICATING THE CLOSED-SHELL INTERACTIONS IN THESE SYSTEMS.

INTRODUCTION: THE INTRAMOLECULAR HYDROGEN BONDING (IMHB) OF (4-SALICYLIDENEIMINO) BENZO-15-CROWN-5 (4SEB15-C-5), INVESTIGATED BASED ON TOPOLOGICAL CHARACTERISTICS OF THE QUANTUM THEORY OF ATOMS IN MOLECULES (qtaim) AND COMPARED TO THE ANALOGOUS PARAMETERS OF SALICYLIDENEANILINE (SAN) AND 2-IMINOMETHYLPHENOL (2IMP). THESE SCHIFF BASES CONTAIN QUASIAROMATIC OR THE RESONANCE ASSISTED HYDROGEN BONDS SYSTEMS (RAHB), WHICH WIDELY DISCUSSED IN THE LITERATURE. THESE COMPOUNDS HAVE THE POTENTIAL APPLICATION AS LIQUID CRYSTALS, NONLINEAR OPTICAL MATERIALS, AND ANTICANCER MEDICINES DUE TO IMHB AND PROTON TRANSFER PROPERTIES.

BISPHOSPHONATES (BPS) ARE ANALOGS OF INORGANIC PYROPHOSPHATE, CONTAINING TWO PHOSPHONATE GROUPS LINKED BY STABLE PHOSPHOETHER BONDS TO A CENTRAL (GEMINAL) CARBON ATOM. THE ABILITY OF BPS TO SELECTIVELY AFFECT OSTEOCLASTS, AND THERE BY INHIBIT BONE RESORPTION, IS BASED ON THEIR THREE-DIMENSIONAL STRUCTURE THAT ALLOWS THE CHELATION OF DIVALENT METAL IONS...

INTRODUCTION: RECENTLY, FULLERENE C60 HAS ALSO RECEIVED MUCH ATTENTION BECAUSE OF ITS UNIQUE BIOLOGICAL ACTIVITIES INCLUDING TOXICITY AND ANTIOXIDANT CAPACITY [1-3]. THE BIOLOGICAL ACTIVITIES OF C60 ARE CRITICALLY ASSOCIATED WITH ITS STRUCTURE, CONCENTRATION, STABILITY AND SIZE DISTRIBUTION IN AQUEOUS MEDIA [4]. HEREIN, THE NATURE OF INTERACTIONS INCLUDING COVALENT/SHARED, INTERMEDIATE AND ELECTROSTATIC WITHIN THE TWO SYSTEMS COMPOSED OF C60 AND TWO CYCLOPHOSPHAMIDE DERIVATIVES WERE STUDIED USING qtaim ANALYSES BY DFT COMPUTATIONS...