XH Groups Research Articles

Echocardiographic assessment of intravenous administration of medetomidine and xylazine hydrochloride at different sedative doses inone-humped camel calves (Camelus dromedarious).

Echocardiography illustrates a convenient and noninvasive tool for measuring cardiac output (CO) changes after administration of sedative drugs, but it is unknown in camelids practice. The aim of present study was to investigate echocardiographic effects of intravenous (IV) injection of medetomidine and xylazine in camel calves. Twenty apparently healthy immature male one-humped camel calves (Camelus dromedarious) were divided into four groups (five animals in each treatment). Medetomidine and xylazine were injected into the left jugular vein at two different doses of 10.00 and 20.00 μg kg-1 and 0.20 and 0.40 mg kg-1, respectively. Effects on some selected echocardiographic parameters were recorded at different intervals, before drug administrations (baseline) and after 3, 60 and 120 min. Data were analyzed by repeated measure, ANOVA test, then relevance and significance were taken as p ≤ 0.05. Significant decrease in fractional shortening percentage (FS%), ejection fraction percentage (EF%), stroke volume (SV), heart rate (HR) and subsequent CO were noticeable 3 min after drug administration in medetomidine high dose (MH), medetomidine low dose (ML) and xylazine high dose (XH) groups (p ≤ 0.05), furthermore at this time significant decrease in left ventricular mass (LVmass) and left ventricular systolic time intervals were seen in these groups, however, in xylazine low dose (XL) group, the lowest level of most echocardiographic parameters were detectable after 60 min. High dose IV injection of medetomidine was associated with significant decrease in most echocardiographic parameters without echocardiographic arrhythmia. Although, ML and XH groups had the same effects on echocardiographic indices but the intensity and duration were less than MH group.

Serum metabolomics reveals compatibility rules of the antidepressant effects of Xiaoyaosan and its efficacy groups

Traditional Chinese medicines (TCMs) have attracted more attentions in the treatment of depression. Xiaoyaosan (XYS), a classic anti-depression TCM prescription, contains eight herbs. However, the compatibility effects of XYS in modern pharmacology need to be investigated in depth. In this study, the chronic unpredictable mild stress (CUMS) depression-like model was constructed. Afterwards, XYS was divided into the Shugan and the Jianpi groups according to the research strategy ofefficacy groups. Meanwhile, a proton nuclear magnetic resonance spectrometry (1H NMR) based serum metabolomics was applied. XYS and its efficacy groups significantly regulated the abnormal levels of differential metabolites related to depression, but to different degrees. Metabolic profiling by orthogonal partial least squares discriminant analysis showed that XYS at high dose (XH) exhibited the strongest effects than other treatment groups. Ten metabolites related to depression were identified as differential metabolites. Besides, relative distance (Rd) was calculated to quantitatively evaluate the effects. We found that XH group had the highest Rd value. Moreover, among the five metabolic pathways of depression, XYS and Jianpi groups significantly regulated all pathways while Shugan group regulated four pathways. These findings lay a solid foundation for comprehensively and deeply understanding the compatibility effects of XYS against depression.

Modeling vibrational anharmonicity in infrared spectra of high frequency vibrations of polyatomic molecules.

In this perspective, we review the challenges of calculating spectra of high-frequency XH vibrations (where X = C, N, or O) of molecules and small clusters. These modes are often coupled to nearly degenerate overtone and combination bands, greatly complicating the interpretation of the spectra. When molecules or clusters contain multiple XH groups, assigning spectra is difficult, especially when multiple conformers are present. We consider approaches appropriate for addressing these difficulties, focusing on systems with more than 15 atoms. At this size, the densities of states of these fundamentals are sufficiently high that it is not possible to calculate eigenstate-resolved spectra. Nonetheless, combining perturbation theory, empirical scalings of vibrational frequencies, and variational treatments of reduced dimensional Hamiltonians, one can identify and model the vibrational coupling pathways that influence observed spectral features. We describe how these methods have evolved through time as electronic structure methods and computational resources have advanced.

Ammonia and phosphine complexes with proton donors. Hydrogen bonding from the backside of the N(P) lone pair

Quantum chemical calculations at the MP2/aug-cc-pVTZ level of theory were carried out to study the molecular Y…HX (Y = N, P; X = O, Cl, F) complexes formed by ammonia and phosphine with H2O, HCl and HF molecules with the orientation of the XH group to the backside of the N(P) lone pair (referred to as anti-complexes). Various methods used for analysis identify the Y…HX intermolecular interaction in the anti-complexes as hydrogen bonding. The NBO analysis shows that the stabilization of the ammonia and phosphine complexes is mainly determined by the nY → σ∗XH interaction between the acceptor lone pair and anti-σ bond XH of the proton donor. The values of topological parameters at the bond critical point for the H…Y contact are typical for neutral H-bonded molecular complexes; while the bridging hydrogen and acceptor atoms demonstrate mutual penetration, and all criteria concerning the integrated properties of the H atom are satisfied. The binding energy in complexes with the anti-orientation of monomers calculated with the BSSE correction was found to vary in the range of 1–3 kcal/mol. The anti-complexes, like typical H-bonded syn-complexes, show lengthening of the covalent XH bond, red-shift in the XH stretching frequency in IR spectra, and downfield chemical shift of the bridging hydrogen atom. The inversion of the NH3(PH3) group leads to transition of the molecular system between the anti- and syn-configurations corresponding to minima on the potential energy surface.

Steric-Hindrance-Induced Regio- and Chemoselective Oxidation of Aromatic Amines.

Unusual regio- and chemoselective oxidation of aromatic amines hindered with ortho substituents (except -NH2, -NHCH3, and -OH) to the corresponding nitro compounds is described by use of nonanebis(peroxoic acid). The mechanistic investigation for selective oxidation of amines ortho-substituted with -NH2 or -OH showed the involvement of H-bonding between the ortho hydrogen of the adjacent -XH group (where X = NH, NR, or O) and an oxygen atom from the diperoxy acid. Various mono- and diamines are oxidized into corresponding mononitro derivatives in high yield and purity without employing any protection strategies. The protocol was also found to successful on the gram scale.

Physical Nature of Substituent Effects in XH/π Interactions.

XH/π interactions (e.g.: CH/π, OH/π, etc.) are ubiquitous in chemical and biochemical contexts. Although there have been many studies of substituent effects in XH/π interactions, there have been only limited systematic studies covering a broad range of substituents. We provide a comprehensive and systematic study aimed at unraveling the nature of aryl substituent effects on model BH/π, CH/π, NH/π, OH/π, and F/π interactions (e.g.: BH3···C6H5Y, CH4···C6H5Y, etc.) based on estimated CCSD(T)/aug-cc-pVTZ interaction energies as well as symmetry-adapted perturbation theory (SAPT) results. We show that the impact of substituents on XH/π interactions depends strongly on the identity of the XH group, and the strength of these effects increases with increasing polarization of the XH bond. Overall, the results are in accord with previous work and follow expected trends from basic physical principles. That is, electrostatic effects dominate the substituent effects for the polar XH/π interactions (NH/π, OH/π, and FH/π), while dispersion effects are more important for the nonpolar BH/π and CH/π interactions. The electrostatic component of these interactions is shown to correlate well with Hammett constants (σm), while accounting for the dispersion component requires consideration of molar refractivities (MR) and interaction distances concurrently. The correlation of the dispersion component of these interactions with MR values alone is rather weak.

Benefits of near-infrared spectroscopy for characterization of selected organo-montmorillonites

The potential of near infrared (NIR) spectroscopy in characterization of organically modified clay minerals is introduced. Selected organo-clays, possibly perspective fillers in clay polymer nanocomposites, were prepared from Na-montmorillonite and different surfactants containing octylammonium chain(s), hexadecylammonium chain(s) or a benzene ring with or without a reactive double bond. Based on the stretching ( ν) and bending ( δ) vibrations observed in the middle IR (MIR) region, the first overtone (2 νXH) and combination ( ν + δ)XH modes of XH groups (X = O, C, N) are identified. The effect of larger alkylammonium cations on the vibrations of Si–O and OH bonds in montmorillonite layers is observed. The changes in the intensity of the ( ν + δ)H 2O band near 5250 cm −1 allows for comparison of the amount of water adsorbed on the montmorillonite surface. The water content decreases with the size of the organic cation reflecting increasing hydrophobicity of the montmorillonite surface. The NIR region shows the 2 νCH 3 and 2 νCH 2 bands in the 5900–5500 cm −1 region, an upward shift is observed for the complex band due to 2 νCH(Ar) of aromatic benzene ring. The NIR spectra are extremely useful in identification of NH 2 +, NH + and vinyl groups, which are difficult to recognize in the MIR spectra of organo-clays due to overlapping with other absorption bands. The intense bands corresponding to overtones and combination vibrations of NH 3 + and NH 2 + groups are found in the 6600–6050 cm −1 and 5000–4600 cm −1 regions, the ( ν + δ)NH + is unambiguously identified near 4750 cm −1. The characteristic band assigned to 2 νCH 2 in H 2C C is detected near 6130 cm −1.

ChemInform Abstract: Model Solvent Systems for QSAR. Part 3. An LSER Analysis of the “ Critical Quartet”. New Light on Hydrogen Bond Strength and Directionality.

An LSER analysis of log P for the ‘critical quartet’ of solvent systems has been carried out using, as initial variables, VI for volume, µ2 for dipolarity, and proton donor ∑α and proton acceptor βf scales based on log Kα and log Kβ respectively. A common data matrix and an unprecedented range of functionalities have been employed. By making the analysis stepwise, starting with the simplest solutes and adding more in order of increasing complexity, we have been able to identify hitherto unrecognised variables and ‘fine-tune’ established ones in such a way as to derive self-consistent proton donor and acceptor values applicable to the whole range of solvent systems. By this ‘LSER in reverse’ we have established, inter alia, the following new facts: (a)βf possesses a constant effective zero whereas that for ∑α is solvent-sensitive; (b) a new term nβf is required for acceptor solutes with two or more available lone pairs; (c) when neither lone pair is available, the acceptor strength of carbonyl is sharply reduced; (d) a second term specific to NH2 is required for ∑α in alkane and chloroform; (e) there is mutual shielding of XH and one lone pair in structures such as CO2H and CONH2; (f) ureas and other structures with parallel NH functions are proton donors of exceptional strength; (g) the acceptor ability of dipolar bases (PO and SO) varies with the solvent system.Cooperativity in solute–solvent bonding exists but takes complex forms, and does not appear strong enough to account e.g. for the hydrogen bonding properties of bulk water and the alcohols, for which mass action appears a likelier explanation. We present evidence (see Appendix) that mass action will most probably explain certain well known anomalies in the apparent proton acceptor ability of water as revealed by partitioning studies.The present results throw new light on previously anomalous octanol–water log P values and can predict f-values for other solvent systems. Most importantly, they provide new information not only on the strength of hydrogen bonding for more than 60 functional groups, but also on its directionality: we are able to predict, with reasonable certainty, which XH groups and lone pairs are actually available for bonding. This information is applicable to water, other solvents, and by implication to the biophase, so should find direct and immediate use in rationalising and quantifying drug–receptor interactions.

Near-infrared spectroscopic analysis of acid-treated organo-clays

AbstractThe potential use of near-infrared (NIR) spectroscopy as a characterization tool for organo-clays would be a great asset but little work has been done in this regard because the application of NIR to clay mineral studies is a relatively new phenomenon. The purpose of this study was to use NIR spectroscopy to investigate the effect of alkylammonium cations on the acid dissolution of a high-charge montmorillonite (SAz-1). Detailed analysis of the spectra of Li+-, TMA+- (tetramethylammonium), and HDTMA+- (hexadecyltrimethylammonium) saturated SAz-1 montmorillonite in the NIR region was achieved by comparing the first overtone (2ν) and combination (ν+δ) bands of XH groups (X = O, C) with the fundamental stretching (ν) and bending (δ) vibrations observed in the mid-infrared (MIR) region. Comprehensive analysis of the vibrational modes of CH3-N, CH3-C, and -CH2-C groups of TMA+ and HDTMA+ cations detected in the MIR and NIR regions was also performed. Both MIR and NIR spectra demonstrated that exchange of Li+ by TMA+ only slightly improved the resistance of SAz-1 layers to dissolution in 6 M HCl at 80°C, while exchange by the larger HDTMA+ cations almost completely protected the montmorillonite layers from acid attack. Use of NIR spectra in reaching these conclusions was crucial. Only in the NIR region could the creation of SiOH groups be monitored, which is an important indicator of the acidification of the montmorillonite surface. The OH-overtone region in the spectra of Li-SAz-1 and TMA-SAz-1 revealed that the SiOH band near 7315 cm−1 increases in intensity with enhanced acid treatment. In contrast, no SiOH groups were identified in the NIR spectra of HDTMA-SAz-1 treated in HCl, indicating that HDTMA+ completely covers the inner and outer surfaces of the montmorillonite and hinders access ofprotons to the Si-O− bonds created upon acid treatment.

Interactions between the Chloride Anion and Aromatic Molecules: Infrared Spectra of the Cl-−C6H5CH3, Cl-−C6H5NH2 and Cl-−C6H5OH Complexes

The Cl- -C6H5CH3*Ar, Cl- -C6H5NH2*Ar, and Cl- -C6H5OH*Ar anion complexes are investigated using infrared photodissociation spectroscopy and ab initio calculations at the MP2/aug-cc-pVDZ level. The results indicate that for Cl- -C6H5NH2 and Cl- -C6H5OH, the Cl- anion is attached to the substituent group by a single near-linear hydrogen bond. For Cl--C6H5CH3, the Cl- is attached to an ortho-hydrogen atom on the aromatic ring and to a hydrogen atom on the methyl group by a weaker hydrogen bond. The principal spectroscopic consequence of the hydrogen-bonding interaction in the three complexes is a red-shift and intensity increase for the CH, NH, and OH stretching modes. Complexities in the infrared spectra in the region of the hydrogen-bonded XH stretch band are associated with Fermi resonances between the hydrogen-stretching vibrational modes and bending overtone and combination levels. There are notable correlations between the vibrational red-shift, the elongation of the H-bonded XH group, and the proton affinity of the aromatic molecule's conjugate base.

Are the solvent effects on H-bonds a cooperativity with van der Waals interactions?

Abstract The solvent influence on the strength of H-bonds, observed by the shift Δν of the OH or NH stretching band, can be described by a solvent parameter LFMj for every solvent j: Δν(B, solventj) = LMFj Δv(B, vapor). This parameter is independent of the H-bond acceptor B and the donor. It is determined for a series of solvents relative to the solvent shift in CCl4. The solvent influences of weak H-bond acceptors are included. The solvent mechanism is very similar to H-bond cooperativity of cations or multiple H-bonds and can be described as a polarization effect of the lone pairs of the bonding XH groups by van der Waals interactions which can be studied by this method. The equations given can predict the not negligible solvent influence on H-bonds. The solvent factors are parallel to the Hildebrand parameters of the solvents or the Gutmann numbers and can be understood in terms of the influence of its intermolecular potentials. There are indications on influences of intermolecular zero point energies in the second approximation.

Accurate measurement of homonuclear coupling constants using JHH-TOCSY

The homonuclear JHH coupling constant is one of the most important NMR parameters. In complex molecules with quite long relaxation times, E.COSY (1) in combination with the DISCO procedure (2) seems to be the best homonuclear method for quantifying J couplings. Other homonuclear methods are z-filtered COSY (3)) J-6 spectroscopy (4)) and selective excitation (5). These methods fail, however, in molecules with short spin-spin relaxation times where the linewidth is in the range of coupling constants. For these situations, some triple-resonance methods have been proposed recently (6-8), which can be used for 15Nand “Ccuenriched peptides and proteins. Their pulse sequences include a heteronuclear coherence transfer from “N to 13C. Additionally the magnetization transfer using a 13C spin lock works well for completely 13C-enriched molecules (9). In these spectra, the signal is split in Fi by the ‘JCH coupling constant, whereas the 3J(HN-H~) coupling constant can be extracted from the displacement in F2. From these methods, precisely estimated coupling constants are obtained, and they are, in distinction to E.COSY, independent of the linewidth. Until now no similar method has been proposed that could be used for molecules at natural abundance. For this purpose, we have developed two new pulse sequences shown in Figs. la and 1 b, called JHH-TOCSY. Sequence 1 a is a H,H correlation and sequence 1 b is a H,X correlation. As for the methods mentioned above, these sequences provide the JHH splitting for XH groups only, whereas XH2 groups show no splitting. For overlapping XH and XH2 groups, and for spectral simplification, XH selection may be used as shown in Fig. 1 c. Figure 1 d shows the 30 extension of sequence 1 a with and without XH selection. JHH-TOCSY is well suited to molecules at natural abundance or for 13Cor “N-monolabeled compounds. In comparison with the triple-resonance methods, the sequences are much shorter, because there is no need for the long 1 /( 2 JCN) delay. The evolution of the magnetization after 2, is as follows (only the relevant operators are shown); cf. Fig. la:

Model solvent systems for QSAR. Part 3. An LSER analysis of the ‘critical quartet.’ New light on hydrogen bond strength and directionality

An LSER analysis of log P for the ‘critical quartet’ of solvent systems has been carried out using, as initial variables, VI for volume, µ2 for dipolarity, and proton donor ∑α and proton acceptor βf scales based on log Kα and log Kβ respectively. A common data matrix and an unprecedented range of functionalities have been employed. By making the analysis stepwise, starting with the simplest solutes and adding more in order of increasing complexity, we have been able to identify hitherto unrecognised variables and ‘fine-tune’ established ones in such a way as to derive self-consistent proton donor and acceptor values applicable to the whole range of solvent systems. By this ‘LSER in reverse’ we have established, inter alia, the following new facts: (a)βf possesses a constant effective zero whereas that for ∑α is solvent-sensitive; (b) a new term nβf is required for acceptor solutes with two or more available lone pairs; (c) when neither lone pair is available, the acceptor strength of carbonyl is sharply reduced; (d) a second term specific to NH2 is required for ∑α in alkane and chloroform; (e) there is mutual shielding of XH and one lone pair in structures such as CO2H and CONH2; (f) ureas and other structures with parallel NH functions are proton donors of exceptional strength; (g) the acceptor ability of dipolar bases (PO and SO) varies with the solvent system.Cooperativity in solute–solvent bonding exists but takes complex forms, and does not appear strong enough to account e.g. for the hydrogen bonding properties of bulk water and the alcohols, for which mass action appears a likelier explanation. We present evidence (see Appendix) that mass action will most probably explain certain well known anomalies in the apparent proton acceptor ability of water as revealed by partitioning studies.The present results throw new light on previously anomalous octanol–water log P values and can predict f-values for other solvent systems. Most importantly, they provide new information not only on the strength of hydrogen bonding for more than 60 functional groups, but also on its directionality: we are able to predict, with reasonable certainty, which XH groups and lone pairs are actually available for bonding. This information is applicable to water, other solvents, and by implication to the biophase, so should find direct and immediate use in rationalising and quantifying drug–receptor interactions.

Inverse proton editing in 1D and 2D spectra by a combination of the SHIPPED and COSY techniques

Inverse NMR spectroscopy leads to increased sensitivity in X, H correlation spectroscopy, since the nucleus with the higher gyromagnetic ratio ( ‘H ) is used both for proton polarization to start the pulse sequence and for detection ( 1, 2). Recently a new pulse sequence has been developed: SHIPPED or selective heteronuclear inverse polarization transfer proton editing (3). The pulse sequence is shown in Fig. la. This inverse pulse sequence allows DEPT editing (4-6) of the ‘H NMR spectrum. One possible application of the SHIPPED experiment is the acquisition of oneand two-dimensional spectra, which contain only signals from XH groups. In order to decouple the X nucleus with the GARPl sequence ( 7), it is necessary to extend the original ID SHIPPED sequence by a second delay A’ = A to refocus the direct heteronuclear coupling. In the last two delays A’ two 180” pulses were inserted to refocus the chemical shifts in order to avoid phase problems (Fig. 1 b) . An interesting idea is to combine a 2D SHIPPED sequence with a COSY transfer. A 2D version of the SHIPPED experiment (Fig. la) replaces the 90” excitation pulse in the H,H COSY.90. This would lead to a 3D experiment, but to avoid this, the second evolution time is converted into a fixed delay AZ. This new variant creates an inverse H, X correlation with a H-relayed transfer (Fig. lc). During ti only the chemical shift of the X nucleus evolves, whereas after the SHIPPED part of the experiment XH magnetization is selected. During A2 the transverse magnetization of the methine proton I, evolves under homonuclear JHH coupling to the relayed proton I,, which is not bound to 13C. The 90” mixing pulse at the end of the sequence transfers the magnetization from spin I, to spin I,. During t2 the transverse magnetization of spin I1 evolves under heteronuclear I JXH coupling. The spectrum obtained shows the doublet signals of the methine protons, which are separated in 1L; by ‘JXH. The signals of the relayed protons show up as singlets. Figure 2 shows a section of a H-relayed SHIPPED-COSY spectrum from the olefinic region of strychnine. The second experiment is a combination of the refocused 1 D SHIPPED and COSY experiments (Fig. Id). After the SHIPPED part of the experiment only transverse magnetization of the methine protons, which evolves during tl under homonuclear JHH and heteronuclear ’ Jxn coupling, is selected. Because of the mixing pulse at the end of tl , polarization is transferred from spin 1, to spin I*, which is not directly bound

The polarity of XH and XM bonds in compounds of the ArXH and ArXM (X = O, S, NR; M = Hg, Sn, Pb, Sb) types and their capacity for coordination and dissociation

The relationship between the values of the σ R + constants of the XMR n and XH groups, reflecting the polarity of the XM and XH bonds, and the capacity of these bonds for heterolytic dissociation in DMSO have been analysed. Linear relations have been established between σ R + and log K d. The factors responsible for the abnormal stability of the SHg and SPb bonds are discussed. It has been shown that the capacity of the XM and XH bonds for dissociation is not determined by the force of the coordination interactions ( K c) between the M or H atoms and DMSO. The parallel pattern of variations in σ R + and K c is observed only in the case of XH acids and their SnPh 3 and PbPh 3 derivatives.

Experimental manifestations of the local-mode description of high energy polyatomic overtone spectra

The local-mode model for polyatomic vibrational overtone absorption is extended to include the effects of nonequivalent XH groups in a molecule, and to describe the major features in the more complex combination regions of the spectrum. The high energy overtones and combinations in the spectra of HCCH, HCCD and HCN are interpreted and used to derive selection rules for the combination regions of the overtone spectra of more complex molecules. CHCl 3 and CH 2Cl 2 combination bands between Δυ CH = 3 and Δυ CH = 4 are used to illustrate the rules. The overtone spectra of methane, ethane, benzene, toluene and o-, m-, and p-xylene are measured and interpreted in terms of the local-mode model. In particular the double band structure of the overtones in these molecules is assigned to the discrete excitation of aryl and alkyl CH oscillators.