Studying Complex Interaction of B2H4 with HOR(R = H, CH3) and Nhn(CH3)3-N (N = 0-3) Molecules

C l i n M e d International Library Citation: Tayebee R, Zabardasti A (2016) Studying Complex Interaction of B2H4 with HOR(R = H, CH3) and Nhn(CH3)3-N (N = 0-3) Molecules. Int J Med Nano Res 3:016 Received: January 09, 2016: Accepted: January 30, 2016: Published: February 02, 2016 Copyright: © 2016 Tayebee R, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Volume 3 | Issue 1


Introduction
Borane complexes are extensively studied and have even been the subject of Nobel Prize by Brown [1].Many scientific data exist that have shown that boron is an essential microelement in animal cells.With the knowledge that borate linkages function in cell-to-cell adhesion, it has been hypothesised that boronates target structural glycoproteins located along the cytoskeletonplasma membrane-cell wall assembly.On the other hand, boron-carrier molecules can be used as a therapeutic mean to fight cancers [2,3].Also, they have been the subject of proton affinity experiments in chemical ionization mass spectrometry.Among non-covalent interactions which have been known in boron chemistry, both dihydrogen and hydrogen bonding patterns are particularly significant [4][5][6][7][8][9].B 2 H 4 , designated as diborane (4), is probably the best known electron-deficient analogue of ethylene [10][11][12][13].B 2 H 4 bears 10 valence electrons for chemical bonding.There are two standard two electron terminal B-H bonds, thus accounting for a total of four electrons.This leaves a total of six electrons to share between the two bridging H and the two B atoms.Consequently, there are two 3c-2e curved 'banana' B-H-B bridging bonds.According to the above illustrations, B 2 H 4 has two types of hydrogen atoms: terminal (H t -B) and bridging (B-H b -B) ones, which differ in nature and characteristics.The bridging hydrogens of B 2 H 4 participate in the electron deficient 'three-center, two-electron bonds'; thus, they bear enough partial positive charge to act as hydrogen bond donor (HBD) to form H b …X (X = N, O) hydrogen bonds with electron donating molecules [6,7,13].On the other hand, recent studies showed that the B-B bond also could act as HBA in the interactions of borane clusters with HBD species to form H…B-B hydrogen bonds [6,13].
From a fundamental point of view, the present work aims to extend the knowledge of the intrinsic activity of H t , H b and B-B bond of diborane as a hydrogen bond acceptor or hydrogen bond donor towards other molecules.For this purpose, we investigated the interaction of B 2 H 4 with H 2 O, CH 3 OH and NH n (CH 3 ) 3-n (n = 0-3) derivatives through theoretical calculations.

Computational Methods
Calculations were performed using the Gaussian 03 system of codes [14].The geometries of the isolated B 2 H 4 , H 2 O, CH 3 OH, and NH n (CH 3 ) 3-n molecules as well as their complexes were fully optimized at the MP2/aug-cc-pVDZ computational level.Harmonic vibrational frequency calculations confirmed the structures as minimal and enabled the evaluation of zero point energy (ZPE).The counterpoise procedure was used to correct the interaction energy for basis set superposition error [15].The AIMAll package was used to obtain bond properties and molecular graphs [16].The natural bond orbitals (NBO) method was implemented within the Gaussian 03 set of codes and was applied to perform NBO analysis [17].

AIM analysis
The atoms in molecules (AIM) theory [16] is applied here to analyze the characteristics of the H…N and H…B-B interactions through studying the location of Bond Critical Points (BCP) with (3,-1) coordinates in the Hessian matrix fitted to the intermolecular contact area.In table 1, results of the QTAIM topological parameters, namely as electronic density (ρ), Laplacian (∇ 2 ρ) and the ratios between kinetic (G) and potential (U) electron energy density [18] are obtained.The last ones are embodied into the QTAIM formalism as follows: This equation indicates which type of interaction may exist between the two nuclei, wherein, the profile of ∇ 2 ρ is embodied into the contribution of G and U.If the potential electron energy density is outweighed by the kinetic, the positive profile of ∇ 2 ρ indicates a depletion of charge density along the inter-nuclear connecting Bond Path (BP) [19].Furthermore, the atomic connection is recognized as close-shell interaction, which is often designated to H-bonds or to other intermolecular weak bound contacts, such as halogen bonds [20], dihydrogen bonds [21][22][23], and π-staking [24].Regarding the values gathered in table 1, first it should be highlighted that the positive values of ∇ 2 ρ ensure that all H-bonds are closed-shell interactions due to the low charge density concentration.The values of -G/U higher than 1, indicate that besides the non-covalent character, the N…H and H…B-B have no tend to be covalent [25].The results due to the intermolecular bond lengths are given in the table 3 and figure 1.In the B 2 H 4 -H 2 O and B 2 H 4 -CH 3 OH complexes, the B1-B4 bond has elongation (0.0015); but, other bonds of B 2 H 4 are shortened (from -0.0009 to -0.0053) upon complex formation.Moreover, a 0.0061 lenthening was observed for O-H bond in these complexes.

Results and Discussion
On the other hand, the N…H b distances in the B 2 H 4 -NH n (CH 3 ) 3-n complexes are in the range of 2.6196 to 2.4997 Å.These distances could be considered as weak bonding interactions between the two components.Comparison of the H b …N distances showed that the obtaine trend was in agreement with the stability of these complexes.
In B 2 H 4 -H 2 O-HB and in B 2 H 4 -CH 3 OH-HB complexes, the B1-B4 bond was elongated (0.0015); but, other bonds of B 2 H 4 were shortenned (-0.0009 to -0.0053) upon complex formation.Also, a 0.0061 Å bond lengthening was observed for O-H bond in these complexes.
The selected vibrational stretching frequencies (cm -1 ) with the corresponding intensities (km.mol -1 ) for the studied complexes are listed in table 4. In the B 2 H 4 -NH n (CH 3 ) 3-n complexes, the B1-B4 vibrational absorption band is less affected by complex formation, thus their observed shifts are negligible.But, in B 2 H 4 -H 2 O-HM and B 2 H 4 -CH 3 OH-HM complexes this bond shows -8 cm -1 red shift which is in agreement with its lengthening due to complex formation.In agreement with lengthening of B1-H5 and B4-H6 bonds, their unsymmetric stretching frequencies, which appeared at 2811 cm -1 in free B 2 H 4 , are red shifted by 6 and 9 cm -1 in B 2 H 4 -NH n (CH 3 ) 3-n complexes.In contrast, unsymmetric stretching frequencies of B1-H5 and B4-H6 showed 5 cm -1 blue shift in B 2 H 4 -H 2 O and B 2 H 4 -CH 3 OH Interaction of B 2 H 4 with H 2 O and CH 3 OH molecules gave the B 2 H 4 -H 2 O and B 2 H 4 -CH 3 OH complexes which have hydrogen bond interactions between B-B bond as HBA and OH functions of H 2 O and CH 3 OH as HBD.Results are demonstrating that later complex has greater stability than the former one.The association of B 2 H 4 and NH n (CH 3 ) 3-n (n = 0-3) derivatives led to the formation of the 1:1 hydrogen bond complexes which has been denoted as B 2 H 4 -NH 3 , B 2 H 4 -NH 2 Me, B 2 H 4 -NHMe 2 and B 2 H 4 -NMe 3 , figure 1.In these complexes hydrogen bond interactions has been found between a bridging proton of the B 2 H 4 as a proton donor and nitrogen atom of amine as a proton acceptor (H b …N

Figure 1 :
Figure 1: Schematic representation of the optimized complexes at MP2/aug-cc-pVDZ computational level.Distances are in Å.

Table 3 :
bonds length of free B 2 H 4 and their variation during intermolecular interactions at MP2/aug-cc-pVDZ.Distances are in Å.