Uracil-water interaction revisited - in search of single H-bonded secondary minima

Monohydrated uracil (UW) complexes are stabilized by both O⋯HO and NH⋯O hydrogen bonds (H-bonds), simultaneously participating in forming three stable cyclic structures. The role and contribution of these individual H-bonds (O⋯HO and NH⋯O) to the stability of the three UW complexes are still not understood, because of the technical problems in obtaining their optimized structures by standard geometry optimization. The present study explores a non-standard approach to identify three single H-bonded local minima structures without imaginary frequency using DFT (M06-2X, B3LYP and B3LYP-D3), MP2 and CCSD(T) theories and Dunning's correlation-consistent aug-cc-pVTZ basis set, in both vacuum and aqueous media (CPCM method). The results reveal that these new structures are very shallow secondary minima between two deep wells or next to a deep well of primary minima (double H-bonded structures) in the potential energy surface. The H-bond energy of these single H-bonded complexes is found to be less sensitive to a wide range (about 15-20 degrees) of O⋯HO and NH⋯O angles, and the linearity is preferred in the stable three single H-bonded structures. The technical method used to locate such a shallow minimum is described in detail and may be useful for identifying local minima in other cases where consecutive multiple H-bonded structures are global minima. Energy decomposition (using symmetry adapted perturbation theory (SAPT)) of interaction energy, electron redistribution, and relevant vibrational modes are discussed.

Electron Correlation or Basis Set Quality: How to Obtain Converged and Accurate NMR Shieldings for the Third-Row Elements?

The quality of theoretical NMR shieldings calculated at the quantum-chemical level depends on various theoretical aspects, of which the basis set type and size are among the most important factors. Nevertheless, not much information is available on the basis set effect on theoretical shieldings of the NMR-active nuclei of the third row. Here, we report on the importance of proper basis set selection to obtain accurate and reliable NMR shielding parameters for nuclei from the third row of the periodic table. All calculations were performed on a set of eleven compounds containing the elements Na, Mg, Al, Si, P, S, or Cl. NMR shielding tensors were calculated using the SCF-HF, DFT-B3LYP, and CCSD(T) methods, combined with the Dunning valence aug-cc-pVXZ, core-valence aug-cc-pCVXZ, Jensen polarized-convergent aug-pcSseg-n and Karlsruhe x2c-Def2 basis set families. We also estimated the complete basis set limit (CBS) values of the NMR parameters. Widely scattered nuclear shieldings were observed for the Dunning polarized-valence basis set, which provides irregular convergence. We show that the use of Dunning core-valence or Jensen basis sets effectively reduces the scatter of theoretical NMR results and leads to their exponential-like convergence to CBS. We also assessed the effect of vibrational, temperature, and relativistic corrections on the predicted shieldings. For systems with single bonds, all corrections are relatively small, amounting to less than 4% of the CCSD(T)/CBS value. Vibrational and temperature corrections were less reliable for H₃PO and HSiCH due to the high anharmonicity of the molecules. An abnormally high relativistic correction was observed for phosphorus in PN, reaching ~20% of the CCSD(T)/CBS value, while the correction was less than 7% for other tested molecules.

On the impact of side methyl groups on the structure and vibrational properties of β-carotenoids. The case of butadiene and isoprene

Theoretical consideration about the impact of methyl groups on the structure and vibrational properties of β-carotenoids, using medium size molecules of trans-butadiene and trans-isoprene, are reported. Density functional theory (DFT) calculations with correlation-consistent and polarization-consistent basis sets were applied to trans-1,3-butadiene and trans-isoprene as the smallest building bricks of β-carotenoids. Their structure and harmonic vibrations were estimated in the complete basis set limit (CBS) using the non-linear least square fit. Optimized geometries and harmonic frequencies, obtained with B3LYP and BLYP density functionals and large basis sets, were favorably reproduced by a significantly faster approach, using a recently modified STO(1M)-3G Slater-type basis set. Selected density functionals with STO(1M)-3G and 6-311++G** basis sets were also successful in predicting β-carotene structures and harmonic vibrations. This work demonstrates the potential applicability of the proposed level of theory for larger molecules, including β-carotenoids, present in numerous natural food sources. The proposed scheme of molecular modeling, applied to biologically active compounds in food, could provide a deeper insight into their function in vivo, which is directly related to their structure and spectroscopic properties. It could also support the experimental qualitative analysis, based on peak assignment of β-carotenoids in various food sources.

On Complex Formation between 5-Fluorouracil and β-Cyclodextrin in Solution and in the Solid State: IR Markers and Detection of Short-Lived Complexes by Diffusion NMR

In this work, the nuclear magnetic resonance (NMR) and IR spectroscopic markers of the complexation between 5-fluorouracil (5-FU) and β-cyclodextrin (β-CD) in solid state and in aqueous solution are investigated. In the attenuated total reflectance(ATR) spectra of 5-FU/β-CD products obtained by physical mixing, kneading and co-precipitation, we have identified the two most promising marker bands that could be used to detect complex formations: the C=O and C-F stretching bands of 5-FU that experience a blue shift by ca. 8 and 2 cm-1 upon complexation. The aqueous solutions were studied by NMR spectroscopy. As routine NMR spectra did not show any signs of complexation, we have analyzed the diffusion attenuation of spin-echo signals and the dependence of the population factor of slowly diffusing components on the diffusion time (diffusion NMR of pulsed-field gradient (PFG) NMR). The analysis has revealed that, at each moment, ~60% of 5-FU molecules form a complex with β-CD and its lifetime is ca. 13.5 ms. It is likely to be an inclusion complex, judging from the independence of the diffusion coefficient of β-CD on complexation. The obtained results could be important for future attempts of finding better methods of targeted anticancer drug delivery.

Factors Governing the Chemical Stability and NMR Parameters of Uracil Tautomers and Its 5-Halogen Derivatives

We report on the density functional theory (DFT) modelling of structural, energetic and NMR parameters of uracil and its derivatives (5-halogenouracil (5XU), X = F, Cl, Br and I) in vacuum and in water using the polarizable continuum model (PCM) and the solvent model density (SMD) approach. On the basis of the obtained results, we conclude that the intramolecular electrostatic interactions are the main factors governing the stability of the six tautomeric forms of uracil and 5XU. Two indices of aromaticity, the harmonic oscillator model of aromaticity (HOMA), satisfying the geometric criterion, and the nuclear independent chemical shift (NICS), were applied to evaluate the aromaticity of uracil and its derivatives in the gas phase and water. The values of these parameters showed that the most stable tautomer is the least aromatic. A good performance of newly designed xOPBE density functional in combination with both large aug-cc-pVQZ and small STO(1M)-3G basis sets for predicting chemical shifts of uracil and 5-fluorouracil in vacuum and water was observed. As a practical alternative for calculating the chemical shifts of challenging heterocyclic compounds, we also propose B3LYP calculations with small STO(1M)-3G basis set. The indirect spin-spin coupling constants predicted by B3LYP/aug-cc-pVQZ(mixed) method reproduce the experimental data for uracil and 5-fluorouracil well.

Local aromaticity mapping in the vicinity of planar and nonplanar molecules

We report on nucleus-independent magnetic shielding (NICS) scans over the centers of six- and five-membered rings in selected metal phthalocyanines (MPc) and fullerene C60 for more accurate characterization of local aromaticity in these compounds. Detailed tests were conducted on model aromatic molecules including benzene, pyrrole, indole, isoindole, and carbazole and subsequently applied to H₂ Pc, ZnPc, Al(OH)Pc, and CuPc. Similar behavior of three selected magnetic probes, Bq, ³ He, and ⁷ Li⁺ , approaching perpendicularly the ring centers, was observed. For better visualization of shielding zone over the centers of aromatic rings, we introduced a simple mathematical procedure: the first and second derivatives of scan curves with respect to magnetic probe position enabled their additional examination. It allowed an easier localization of curve minimum and discrimination between areas in space varying by the magnetic field magnitude and to illustrate local aromaticity of two different kinds of rings in MPc with better resolution. Our results supported earlier reports on very low aromaticity indexes of pyrrole ring incorporated into MPc and significant aromaticity of the central macrocycle. No direct dependence between harmonic oscillator model of aromaticity and NICS was observed. Instead, a correlation between position of scan curve minimum and its magnitude were observed. In addition, the NICS values and ³ He chemical shifts in the middle of neutral C60 and C60^6- anion agreed well with the reported experimental NMR values for He@C60 and He@C60^6- .

Convergence of nuclear magnetic shieldings and one-bond 1 J(11 B1 H) indirect spin-spin coupling constants in small boron molecules

Self-consistent field Hartree-Fock, density functional theory, and coupled-cluster calculations of the nuclear magnetic shielding constants of BH and BH₃ molecules have been conducted to characterize the convergence of individual results obtained with correlation-consistent and polarization-consistent basis sets. The individual ¹¹ B and ¹ H NMR parameters were estimated in the complete basis set limit and compared with benchmark results. Only the KT3 density functional accurately reproduced ¹¹ B shielding in BH molecule.

Toward engineering efficient peptidomimetics. Screening conformational landscape of two modified dehydroaminoacids

Effective peptidomimetics should posses structural rigidity and appropriate interaction pattern leading to potential spatial and electronic matching to the target receptor site. Rational design of such small bioactive molecules could push chemical synthesis and molecular modeling toward faster progress in medicinal chemistry. Conformational properties of N-t-butoxycarbonyl-glycine-(E/Z)-dehydrophenylalanine N',N'-dimethylamides (Boc-Gly-(E/Z)-ΔPhe-NMe2 ) in chloroform were studied by NMR and IR spectroscopy. The experimental findings were supported by extensive calculations at DFT(B3LYP, M06-2X) and MP2 levels of theory and the β-turn tendency for both isomers of the studied dipeptide were determined in vacuum and in solution. The theoretical data and experimental IR results were used as an additional information for the NMR-based determination of the detailed solution conformations of the peptides. The obtained results reveal that N-methylation of C-terminal amide group changes dramatically the conformational properties of studied dehydropeptides. Theoretical conformational analysis reveals that the tendency to adopt β-turn conformations is much weaker for the N-methylated Z isomer (Boc-Gly-(Z)-ΔPhe-NMe2 ), both in vacuum and in polar environment. On the contrary, N-methylated E isomer (Boc-Gly-(E)-ΔPhe-NMe2 ) can easily adopt β-turn conformation, but the backbone torsion angles (φ1, ψ1, φ2, ψ2) are off the limits for common β-turn types.

DFT studies on the structural and vibrational properties of polyenes

Detailed density functional theory (DFT) calculations on the structure and harmonic frequencies of model all-trans and all-cis polyenes were undertaken. For the first time, we report on the convergence of selected B3LYP/6-311++G** and BLYP/6-311++G** calculated structural parameters resulting from a systematic increase in polyene size (chains containing 2 to 14 C = C units). The limiting values of the structural parameters for very long chains were estimated using simple three-parameter empirical formulae. BLYP/6-311++G** calculated ν(C = C) and ν(C–C) frequencies for all-trans and all-cis polyenes containing up to 14 carbon–carbon double bonds were used to estimate these values for very long chains. Correction of raw, unscaled vibrational data was performed by comparing theoretical and experimental wavenumbers for polyenes chains containing 3 to 12 conjugated C = C units with both ends substituted by tert-butyl groups. The corrected ν(C = C) and ν(C–C) wavenumbers for all-trans molecules were used to estimate the presence of 9 – 12 C = C units in all-trans polyene pigment in red coral.

Graphical abstract

Predicting the structure and vibrational frequencies of ethylene using harmonic and anharmonic approaches at the Kohn-Sham complete basis set limit

In this work, regular convergence patterns of the structural, harmonic, and VPT2-calculated anharmonic vibrational parameters of ethylene towards the Kohn–Sham complete basis set (KS CBS) limit are demonstrated for the first time. The performance of the VPT2 scheme implemented using density functional theory (DFT-BLYP and DFT-B3LYP) in combination with two Pople basis sets (6-311++G** and 6-311++G(3df,2pd)), the polarization-consistent basis sets pc-n, aug-pc-n, and pcseg-n (n = 0, 1, 2, 3, 4), and the correlation-consistent basis sets cc-pVXZ and aug-cc-pVXZ (X = D, T, Q, 5, 6) was tested.

The BLYP-calculated harmonic frequencies were found to be markedly closer than the B3LYP-calculated harmonic frequencies to the experimentally derived values, while the calculated anharmonic frequencies consistently underestimated the observed wavenumbers. The different basis set families gave very similar estimated values for the CBS parameters. The anharmonic frequencies calculated with B3LYP/aug-pc-3 were consistently significantly higher than those obtained with the pc-3 basis set; applying the aug-pcseg-n basis set family alleviated this problem. Utilization of B3LYP/aug-pcseg-n basis sets instead of B3LYP/aug-cc-pVXZ, which is computationally less expensive, is suggested for medium-sized molecules. Harmonic BLYP/pc-2 calculations produced fairly accurate ethylene frequencies.

Graphical Abstract

In this study, the performance of the VPT2 scheme implemented using density functional theory (DFT-BLYP and DFT-B3LYP) in combination with the polarization-consistent basis sets pc-n, aug-pc-n, and pcseg-n (n = 0, 1, 2, 3, 4), and the correlation-consistent basis sets cc-pVXZ and aug-cc-pVXZ (X = D, T, Q, 5, and 6) was tested. For the first time, we demonstrated regular convergence patterns of the structural, harmonic, and VPT2-calculated anharmonic vibrational parameters of ethylene towards the Kohn–Sham complete basis set (KS CBS) limit

Collapse

Questing behavior of Dermacentor reticulatus adults (Acari: Amblyommidae) during diurnal activity periods in eastern Poland

Studies on diurnal activity and factors affecting the questing behavior in Dermacentor reticulatus (F.) adults were conducted in an open-type habitat in eastern Poland (51 degrees 15' N, 22 degrees 36' E). Observations, for 25 min each, were made at 2-h intervals between 1000 and 1800 hours, during the autumn (from late September to mid-October 2000) and spring (from late April to mid-May 2001) activity peaks. The questing behavior of adult D. reticulatus ticks depended on the time of the day and season. The autumn activity was higher than that in spring, yet both these periods were characterized by a rising trend from the morning to early afternoon with a peak at approximately 1400 hours (on average 40 and 30 specimens per one collection, respectively). In spring, the high activity (on average 31.8 specimens/ collection) persisted until late afternoon (1800 hours), while in the autumn period it declined before nightfall (on average 21.4 specimens/collection at 1800 hours). Females predominated over males in both seasonal periods of activity and greater differences in the sex ratio were recorded in the spring. We found a negative correlation between the diurnal activity of the adult ticks and temperature and between the number of active ticks and the length of day both in the autumn and spring. However, no statistically significant correlation was demonstrated between the diurnal activity of adult ticks and humidity. The investigations show that, in addition to environmental factors, tick host-seeking behavior is dependent on the activity of their hosts and biological traits of this species.

Effects of side-chain orientation on the backbone conformation of the dehydrophenylalanine residue. Theoretical and X-ray study

Two E isomers of α,β-dehydro-phenylalanine, Ac-(E)-ΔPhe-NHMe (1a) and Ac-(E)-ΔPhe-NMe(2) (2a), have been synthesized and their low temperature structures determined by single-crystal X-ray diffraction. A systematic theoretical analysis was performed on these molecules and their Z isomers (1b and 2b). The ϕ,ψ potential energy surfaces were calculated at the MP2/6-31+G(d,p) and B3LYP/6-31+G(d,p) levels in the gas phase and at the B3LYP/6-31+G(d,p) level in the chloroform and water solutions with the SCRF-PCM method. All minima were fully optimized by the MP2 and DFT methods, and their relative stabilities were analyzed in terms of π-conjugation, internal H-bonds, and dipole-dipole interactions between carbonyl groups. The results indicate that all the studied compounds can adopt the conformation H (ϕ, ψ ≈ ±40°, ∓120°) which is atypical for standard amino acids residues. A different arrangement of the side chain in the E and Z isomers causes them to have different conformational preferences. In the presence of a polar solvent both Z isomers of ΔPhe (1b and 2b) are found to adopt the 3(10)-helical conformation (left- and right-handed are equally likely). On the other hand, this conformation is not accessible or highly energetic for E isomers of ΔPhe (1a and 2a). Those isomers have an intrinsic inclination to have an extended conformation. The conformational space of the Z isomers is much more restricted than that of the E derivative both in the gas phase and in solution. In the gas phase the E isomers of ΔPhe have lower energies than the Z ones, but in the aqueous solution the energy order is reversed.

Extrapolation of water and formaldehyde harmonic and anharmonic frequencies to the B3LYP/CBS limit using polarization consistent basis sets

The harmonic and anharmonic frequencies of fundamental vibrations in formaldehyde and water were successfully estimated using the B3LYP Kohn-Sham limit. The results obtained with polarization- and correlation-consistent basis sets were fitted with a two-parameter formula. Anharmonic corrections were obtained by a second order perturbation treatment (PT2). We compared the performance of the PT2 scheme on the two title molecules using SCF, MP2 and DFT (BLYP, B3LYP, PBE and B3PW91 functionals) methods combined with polarization consistent pc-n (n = 0, 1, 2, 3, 4) basis sets, Dunning’s basis sets (aug)-cc-pVXZ where X = D, T, Q, 5, 6 and Pople’s basis sets up to 6-311++G(3df,2pd). The influence of SCF convergence level and density grid size on the root mean square of harmonic and anharmonic frequency deviations from experimental values was tested. The wavenumber of formaldehyde CH₂ anharmonic asymmetric stretching mode is very sensitive to grid size for large basis sets; this effect is not observed for harmonic modes. BLYP-calculated anharmonic frequencies consistently underestimate observed wavenumbers. On the basis of formaldehyde anharmonic frequencies, we show that increasing the Pople basis set size does not always lead to improved agreement between anharmonic frequencies and experimental values.

Figure

Sensitivity of water B3LYP calculated harmonic and anharmonic v_s(OH) frequencies on selected Pople and polarization consistent basis sets size. The results for pc-n basis sets were fitted with two parameter formula and the CBS(2,3,4) estimated

Collapse

Spectroscopic study of fluorescent naphthoylenebenzimidazole derivatives in Langmuir-Blodgett films: self-aggregates formation

Some derivatives of naphthoylenebenzimidazole as well as their mixtures with arachidic acid have been incorporated in Langmuir and Langmuir-Blodgett films. Surface pressure versus mean molecular area isotherms for Langmuir films were recorded and the organization of molecules at the air-water interface has been estimated. Absorption spectra in situ for Langmuir films and both absorption and fluorescence spectra for LB films have been recorded. The results obtained from spectroscopic studies have led to conclusions about formation of self-aggregates by dye molecules at interfaces. In the ground electronic state some fraction of the I- and J-type aggregates have been created, whereas in the excited state the creation of genuine excimers has been observed.

The effect of beta-methylation on the conformation of alpha, beta-dehydrophenylalanine: a DFT study

Dehydroamino acids are non-coded amino acids that offer unique conformational properties. Dehydrophenylalanine (DeltaPhe) is most commonly used to modify bioactive peptides to constrain the topography of the phenyl ring in the side chain, which commonly serves as a pharmacophore. The Ramachandran maps (in the gas phase and in CHCl(3) mimicking environments) of DeltaPhe analogues with methyl groups at the beta position of the side chain as well as at the C-terminal amide were calculated using the B3LYP/6-31 + G** method. Unexpectedly, beta-methylation alone results in an increase of conformational freedom of the affected DeltaPhe residue. However, further modification by introducing an additional methyl group at C-terminal methyl amide results in a steric crowding that fixes the torsion angle psi of all conformers to the value 123 degrees , regardless of the Z or E position of the phenyl ring. The number of conformers is reduced and the accessible conformational space of the residues is very limited. In particular, (Z)-Delta(betaMe)Phe with the tertiary C-terminal amide can be classified as the amino acid derivative that has a single conformational state as it seems to adopt only the beta conformation.

Structural changes in the salivary glands of Ixodes ricinus larvae

The authors analysed the structure of Ixodes ricinus (L.) larvae in specimens immediately after leaving the egg sheaths, in those which have not fed for 2 months after hatching, and in feeding larvae on the second day of feeding. The results showed that salivary glands in tick larvae are formed by alveoli aligned in strands on both sides of the central nervous system. These alveoli open into central efferent ducts via short ducts. The constituent elements of salivary glands include pyramidal alveoli (with numerous lipid droplets) and granular alveoli of varied structure. It is worth noting that salivary alveoli containing secretory material are present even in the larvae which had just left egg sheaths and were still endowed with deutoplasm.

[Morphometric features of tarsus in Dermacentor reticulatus (Fabricius, 1794) (Acari: Ixodida: Ixodidae) larvae from Polish and Slovakian populations]

Dermacentor reticulatus is widely distributed dangerous tick that usually lives in the river valleys, boggy forests, meadows, and wooded pastures. Tick populations from various regions may exhibit morphological differences. In our study we compared morphometric features of tarsus in larvae D. reticulatus from Polish and Slovakian populations. I tarsus width, III tarsus length, and length of dorsal setae of I tarsus were significantly higher in Polish populations. Indices of width to length of tarsus I and tarsus III were also significantly different in both populations. The other examined morphologic features were similar, what may result from the same environmental conditions of both populations.

[Pediculosis in rural schools of Lublin Province]

The aim of the work was to study the prevalence of pediculosis capitis among schoolchildren in rural areas of Lublin Province in Eastern Poland and to examine its correlation with socio-economic conditions. A group of 42759 schoolchildren aged between 6 and 15 years from 52 rural primary schools were examined. The level of unemployment, number of physicians and number of nurses per 10000 inhabitants were examined in the area of experiment. We achieved the following results: a total of 682 children were found to be infested with Pediculus humanus capitis, mean prevalence was 1.6%. The girls were more frequently infected than boys (75% for girls and 24% for boys). The children most frequently affected were those aged 6 (1.6%) and 8 to 12 years (1.6-2.1%). The children least affected were those aged 13 to 14 years (0.8-1.1%). The infestation rate was strictly correlated with the number of nurses per 10000 inhabitants. There was no relationship between the level of unemployment or the number of physicians and the infestation rate on experimental area. Our investigations seems to confirme that the prevalence of P. h. capitis is influenced by the level of primary health care, particulary quality of school nurses' work.

Sense organs in post-embryonic stages of Hyalomma marginatum marginatum Koch, 1844 (Acari: Ixodida: Ixodidae). II. Palpal organ

Light microscopy and scanning electron microscopy (SEM) studies show the differences in structure, number and topography of terminal setae in the palpal organ in different stages of Hyalomma marginatum marginatum Koch, 1844. The palpal organ contains eight terminal setae in larvae and nymphs, and ten setae in adults. The length of these setae increases in the course of post-embryonic development. Other setae on palpal segments also undergo quantitative and morphological changes.

Experimental teratogeny in the tick Hyalomma marginatum marginatum (Acari: Ixodida: Ixodidae): effect of high humidity on embryonic development

The effect of 90% RH on the embryonic development of Hyalomma marginatum marginatum Koch was investigated at 25 degrees C. Under the influence of this factor, 2.1% dead eggs, 13.0% dead embryos, 6.9% abnormally hatched larvae, 0.2% larvae with malformations, and 77.8% normal larvae appeared. The embryos died during the cleavage of nuclei, the formation of the blastoderm, the formation of the germ band and its metamerization, and the differentiation of the leg anlagen. Egg hatch was also inhibited in various phases. Various kinds of anomalies were observed in larvae of Hyalomma m. marginatum. Most teratological changes (70.8%) occurred within the idiosoma. They were hetromorphose (32.6%), oligomely (15.4%), heterosymely (12.3%), symely (1.5%), atrophy (6.1%), and ectomely (3.1%). Anomalies within the gnathosoma occurred rarely (3.1%). As many as 26.2% larvae had composite anomalies (oligomely, heterosymely, atrophy) together. They contained various structures of the gnathosoma or idiosoma. These anomalies decreased the survival rate of the larvae. The investigations showed that during the formation of the blastoderm, the formation of the germ band and its metamerization the embryos have the largest susceptibility of being affected by high humidity. Some anomalies in specimens collected from nature may develop under influence of unfavorable humidity levels.

[Toxicoses of ticks (Acari: Ixodida)]

Toxins have been shown to present in the salivary glands, whole body extracts, and eggs of ticks. They cause histological lesions in the skin, and in various organs of tick hosts. Among toxicoses, tick paralysis is of the greatest medical and veterinary importance. Toxins are secreted by cells "b" of acinus II in salivary glands during tick feeding.

[Physiology of ticks (Ixodida) in non-parasitic phase of life cycle]

Non-parasitic phase of ticks is the most critical period of their life cycle. During off host period the ticks must maintain the water homeostasis and must find a host for feeding. Body water homeostasis is one of the most important processes that influences tick survival in nature and transmission of pathogens. Structure of intergument, particularly the waxy lipids in the epicuticle, and structure of peritremes restrict the loss of water from tick body. The water losses may be compensated by uptake of water vapour from the atmosphere. The critical equilibrium humidity of tick species of Ixodidae family range from 70 to 96% r.h. During non-feeding period, behaviour of ticks contributes to the maintenance of body water. The ticks aviod the microhabitats where loss of water may be accelerated.

[Host location by ticks (Acari: Ixodida)]

Ticks respond to host stimuli, such as higher CO2 concentrations,vibrations, odour, touch, radiant heat ad kairomones. The behaviour al reactions to these host stimuli vary among tick species. Among these arthropods hunter (actively running in the direction of host) or ambusher ticks (passively waiting for host on the vegetation) occur. Hallers organ, palpal organ, cheliceral organ and receptors on scutum and alloscutum are involved in tick feeding behaviour.

Sense organs in post-embryonic stages of Hyalomma marginatum marginatum Koch, 1844 (Acari: Ixodida: Ixodidae). I. Tarsal sensory system

Light and scanning electron microscopic studies showed the differences in morphology and in size of Haller's organ in larvae, nymphs and adults (females and males) of Hyalomma marginatum marginatum Koch, 1844. The length of the anterior pit setae increases during post-embryonic development. The localization of these setae is the same in all stages. Six setae (one porose seta, two grooved setae, two fine setae, one conical seta) contain anterior pit of various developmental stages. In nymphs and adults more numerous pores appear on the wall surface of porose seta than in the larval stage. The structure of the capsule roof also differs in various developmental stages. Haller's organ of Hyalomma m. marginatum shows great degree of morphological development which is connected with the complicated life cycle and feeding behaviour of this tick species.

[The effect of technopathologically limited stress factors on the fertility of cattle]

The influence of purulent claw-diseases on the development of uterus infections, its involution and ovary dysfunctions (acyclia, cysts) was examined. It was shown that A. pyogenes, Ps. aeruginosa, Fus. necrophorum and other microorganisms involved in these lesions are potential sources for the infections of the uterus. In comparison with the controls the frequency of endometritis was twice in the group with claw-problems. Similar differences existed in the involution-time of the uterus or its atonia, acyclia and the development of ovarian cysts (p less than 0.01). The Index of insemination was elevated by about 65%.