Prediction and experimental validation of solid solutions and isopolymorphs of cytosine/5-flucytosine.

A computational search for polymorphs of cytosine, 5-flucytosine and a 1 : 1 mixture of the two substances not only rationalised the preferred packing arrangements but also enabled the finding and characterisation of cytosine/5-flucytosine solid solutions. The structures of the new solid forms were determined by combining laboratory powder X-ray diffraction data and computational modelling.

Copper(i)oxide microparticles - synthesis and antimicrobial finishing of textiles.

Copper containing particles are of high interest to provide antibacterial activity to textiles for medical products, hygiene application or where odor formation as result of bacterial activity has to be controlled. Cu(i)oxide microparticles with a rather uniform diameter between 1.5 and 2 µm can be prepared by controlled reduction of alkaline Cu(ii)-tartaric acid complexes. Such particles can be bound to textile surfaces by means of a pigment binder system used in pigment dyeing. By a simple pad-dry process textile fabrics with a Cu-content of 250-270 mg Cu per kg fabric could be prepared. The samples (fabrics) exhibited a reduction in viability of 100% for Staphylococcus aureus and 84% for Klebsiella pneumonia as estimated by the ASTM E2149 antimicrobial test. Simulated wash procedures led to a reduction in Cu-content to 60-50% of the initial value. Reduction in viability remained at 99% for Staphylococcus aureus and 78% for Klebsiella pneumoniae. The new process is of high value to impart antimicrobial properties to textile products because an antimicrobial product with good wash permanence can be delivered using rather simple processing and ordinary chemicals.

Comparison of NIR chemical imaging with conventional NIR, Raman and ATR-IR spectroscopy for quantification of furosemide crystal polymorphs in ternary powder mixtures.

The aim of this study was to evaluate the ability of near-infrared chemical imaging (NIR-CI), near-infrared (NIR), Raman and attenuated-total-reflectance infrared (ATR-IR) spectroscopy to quantify three polymorphic forms (I, II, III) of furosemide in ternary powder mixtures. For this purpose, partial least-squares (PLS) regression models were developed, and different data preprocessing algorithms such as normalization, standard normal variate (SNV), multiplicative scatter correction (MSC) and 1st to 3rd derivatives were applied to reduce the influence of systematic disturbances. The performance of the methods was evaluated by comparison of the standard error of cross-validation (SECV), R(2), and the ratio performance deviation (RPD). Limits of detection (LOD) and limits of quantification (LOQ) of all methods were determined. For NIR-CI, a SECVcorr-spec and a SECVsingle-pixel corrected were calculated to assess the loss of accuracy by taking advantage of the spatial information. NIR-CI showed a SECVcorr-spec (SECVsingle-pixel corrected) of 2.82% (3.71%), 3.49% (4.65%), and 4.10% (5.06%) for form I, II, III. NIR had a SECV of 2.98%, 3.62%, and 2.75%, and Raman reached 3.25%, 3.08%, and 3.18%. The SECV of the ATR-IR models were 7.46%, 7.18%, and 12.08%. This study proves that NIR-CI, NIR, and Raman are well suited to quantify forms I-III of furosemide in ternary mixtures. Because of the pressure-dependent conversion of form II to form I, ATR-IR was found to be less appropriate for an accurate quantification of the mixtures. In this study, the capability of NIR-CI for the quantification of polymorphic ternary mixtures was compared with conventional spectroscopic techniques for the first time. For this purpose, a new way of spectra selection was chosen, and two kinds of SECVs were calculated to achieve a better comparability of NIR-CI to NIR, Raman, and ATR-IR.

Dehydration kinetics and crystal water dynamics of carbamazepine dihydrate.

PURPOSE: To investigate the dehydration of carbamazepine dihydrate, combining kinetics and crystal water dynamics with electronic structure calculations. METHODS: Thermal microscopy, moisture sorption, and thermogravimetric analysis (TGA) were applied to evaluate the effects on relative humidity (RH) and temperature, while crystal water dynamics were monitored by 2D-FTIR correlation spectroscopy (2DCOS) and the nature of the H-bonding network was investigated by 3D-periodic DFT calculations. RESULTS: It was found that the dihydrate is unstable below 40% RH and/or above the glass transition temperature (T g ∼ 53°C). At room temperature, amorphous carbamazepine is formed at RH ∼ 0%, form I at RH ∼ 10%, and mixtures of forms I and III at higher RH. Above the T g , the dehydration yields partially crystalline mixtures of forms I and IV between 50­100°C, and form I above 100°C. In all cases, the amorphous product crystallizes to form IV. Thermal analysis and 2DCOS revealed a biphasic dehydration process. Kinetic modelling suggests a diffusion-controlled dehydration below T g and reaction interface-controlled kinetics above T g . CONCLUSIONS: The dehydration consists of two overlapping water removal processes, with the water molecule attached to the amide C=O departing faster, probably due to the destabilizing effect of anti-bonding interactions between the water H1s and the carbonyl O2p orbital.

Near-infrared reflection spectroscopy (NIRS) as a successful tool for simultaneous identification and particle size determination of amoxicillin trihydrate.

A successful application of NIR spectroscopy (NIRS) in combination with multivariate data analysis (MVA) for the simultaneous identification and particle size determination of amoxicillin trihydrate particles was developed. Particle size analysis was ascertained by NIRS in diffuse reflection mode on different particle size fractions of amoxicillin trihydrate with D90 particle diameters ranging from 6.9 to 21.7 µm. The present problem of fractionating the powder into good enough size fractions to achieve a stable calibration model was solved. By probing dried suspensions measurement parameters were optimized and further combined with the best suitable chemometric operations. Thereby the quality of established regression models could be improved considerably. A linear coherence between particle size and absorbance signal was found at specific wavenumbers. Satisfactory clustering by particle size was achieved by principal component analysis (PCA) whereas partial least squares regression (PLSR) and principal component regression (PCR) was compared for quantitatively calibrating the NIRS data. PLSR turned out to predict unknown test samples slightly better than PCR.

Characterization of four crystal polymorphs and a monohydrate of s-bupivacaine hydrochloride (levobupivacaine hydrochloride).

Five crystal forms of the amide-type local anesthetic S-bupivacaine hydrochloride (levobupivacaine) were prepared and characterized by means of thermal analytical methods, FTIR- and Raman-spectroscopy, powder X-ray diffractometry, and moisture sorption analysis. Commercial lots of the substance may consist of form A degrees , the thermodynamically stable form at 20 degrees C, and/or the metastable form C. Form A degrees shows a highly reversible transformation into form B (T(trs): 85.3 degrees C) with a transition enthalpy of 4.6 kJ mol(-1). The hysteresis between the experimental transition temperatures is 3.5 K, indicating a very weak kinetic control. The hydrate shows a variable water content (0.71-1.14 mol/mol) between 10% and 90% relative humidity (RH) and dehydrates to form C under dry conditions or at elevated temperatures. All anhydrous forms transform to the hydrate at and above 90% RH (25 degrees C). Form C slowly converts to form A degrees on storage and is the polymorph with the highest hygroscopicity. At higher temperatures all forms transform into form D, which is kinetically stable at 20 degrees C. It is concluded that the forms A degrees , B, and D are enantiotropically related, whereas form C shows a monotropic relationship to these forms and is metastable in the entire temperature range.

Dynamic moisture sorption and desorption of standard and silicified microcrystalline cellulose.

Moisture sorption and desorption isotherms of standard and silicified microcrystalline cellulose (MCC and SMCC) were determined using an automatic multi-sample gravimetric analyzer, and compared by fitting different kinetic models, including the excess surface work model (ESW), the BET and GAB model, Young and Nelson model and recently developed parallel exponential kinetics (PEK) model. It was found that silicification affects the moisture sorption and desorption properties of SMCC mainly at high relative humidity (above 50% and 70%, respectively). In general, the differences in the moisture sorption and desorption properties of MCC and SMCC can be elucidated by the different kinetic models. Particularly the PEK model shows that hysteresis is related primarily to a fast sorption process, which corresponds to bound water, and secondarily to a slow process, which corresponds to sorption of free water and that SMCC acquires more water than MCC at RH higher than 50% by the slow (secondary) sorption process. A possible mechanism for this process is presumably the hydrolysis of SiO2 particles and formation of silanol groups that act as a water reservoir, preventing the accumulation of more water in the polymer matrix and thus may be protecting the structure of SMCC from undergoing irreversible structural changes that would impair its performance as an excipient.

Theoretical approaches to physical transformations of active pharmaceutical ingredients during manufacturing processes.

Processing-induced transformations (PITs) during pharmaceutical manufacturing are well known but difficult to predict and often difficult to control. This review of the concepts of transformations is couched in terms of the issues associated with identifying rate-controlling events from the materials side and the processing side. Specifically, the approach is reconciling the characteristic time scale of the structural change(s) in the material with the time scale of the processing-induced stress. This is definitely a model (or rather a melding of a group of existing theories) in development. This overview is a 'snapshot' of the authors' attempts to identify the categories of existing theories needed to encompass all of the relevant events for each possible PIT. The ultimate goal is to establish a framework of concepts and theories for consideration, discussion, and modeling of PITs as well as to locate much of the relevant literature in the framework.

Substance P and vasoactive intestinal polypeptide in the streptozotocin-induced diabetic rat retina.

PURPOSE: Little knowledge exists about how neurotransmitters behave in the diabetic retina. In this study, the authors measured the concentration of two neuropeptides, substance P and vasoactive intestinal polypeptide, in the streptozotocin-induced diabetic rat retina in a time-dependent manner. METHODS: The retinas of 1-, 3-, 5-, 8-, and 12-week diabetic rats were processed using a highly sensitive radioimmunoassay for both substance P and vasoactive intestinal polypeptide. Furthermore, the peptide-immunoreactivities were characterized by high-pressure liquid chromatography. RESULTS: Substance P and vasoactive intestinal polypeptide were found to be significantly reduced with a maximum decrease of 28.6% (+/-6.7) and 64.5% (+/-10.7) after 5 weeks, respectively. The peptide-immunoreactivities were found in a major peak coeluting with the synthetic peptides indicating that the quantitative values measured by radioimmunoassay represent the authentic peptides. CONCLUSIONS: The reduction of substance P and vasoactive intestinal polypeptide is in clear contrast to the amino acid transmitters GABA and glycine, which have been shown to be elevated in this early stage of diabetic retinopathy. This finding is important for three reasons: First, the decrease may result in reduced excitability of inner retinal neurons, as both peptides are known to modulate the excitability of these neurons; second, the decrease may be the consequence of a depressing and/or damaging effect by excitotoxins; and third, it may help explain why neovascularizations do not occur in this animal model, although VEGF is massively upregulated, as substance P is a very potent vascular growth factor.

Conformational color polymorphism and control of crystallization of 5-methyl-2-[(4-methyl-2-nitrophenyl)amino]-3-thiophenecarbonitrile.

5-Methyl-2-[(4-methyl-2-nitrophenyl)amino]-3-thiophenecarbonitrile is an example of conformational and color polymorphism. The compound crystallizes in red (R), dark red (DR), light red (LR), and orange (O) modifications. There are two specific goals for this study. One is to characterize the complex thermodynamic relationship among these four known forms, and the other is to use the knowledge of the thermodynamic relationship to control the crystallization of these forms. The different forms were characterized by X-ray powder diffractometry as well as Fourier-transform infrared (FT-IR) and Raman spectroscopy; their complex thermodynamic relationships were determined by thermal analysis, solubility measurements, and slurry conversion studies. According to the solubility results, all forms are enantiotropically related: R is the thermodynamically most stable form above 60 degrees C, O is the most stable form between room temperature and 60 degrees C, LR is the most stable form below -15 degrees C, and DR is metastable throughout the entire temperature range. DR, LR, and O have very similar free energy at ambient temperature, which is the reason for the complex transition behavior. Finally, a schematic energy-temperature diagram was constructed that combines all experimental data in a comprehensive thermodynamic picture and provides insights into how to control the crystallization of the individual forms.

LST1: a gene with extensive alternative splicing and immunomodulatory function.

The gene of the leukocyte-specific transcript (LST1) is encoded within the TNF region of the human MHC. The LST1 gene is constitutively expressed in leukocytes and dendritic cells, and it is characterized by extensive alternative splicing. We identified 7 different LST1 splice variants in PBMC; thus, 14 LST1 splice variants (LST1/A-LST1/N) have been detected in various cell types. These isoforms code for transmembrane as well as soluble LST1 proteins characterized by two alternative open reading frames at their 3' end. We demonstrate the presence of the transmembrane variant LST1/C on the cell surface of the monocytic cell lines U937 and THP1. Recombinant expression of LST1/C permitted its profound inhibitory effect on lymphocyte proliferation to be observed. In contrast, the alternative transmembrane variant LST1/A, the extracellular domain of which shows no amino acid sequence homology to LST1/C exerted a weaker but similar inhibitory effect on PBMC. These data demonstrate the protein expression of LST1 on the cell surface of mononuclear cells, and they show an inhibitory effect on lymphocyte proliferation of two LST1 proteins although they have only a very short amino acid homology.

Expression and regulation of the thrombopoietin receptor variants MPLP and MPLK in PBMC.

The human c-mpl proto-oncogene encodes the receptor for thrombopoietin (TPO), which plays a central role in magakaryopoiesis and platelet production. Recent results showed that c-mpl mRNA expression is restricted to CD34(+) cells, megakaryocytes, and platelets. The authors analysed mRNA expression by reverse transcription and PCR (RT-PCR) of the transmembrane Mpl variants, MPLK and MPLP, in magakaryocytic cell lines, peripheral blood mononuclear cells (PBMC), lymphocytes, and monocytes. Transcription of both Mpl variants was detected in freshly isolated PBMC and the megakaryocytic cell line, DAMI, whereas none could be detected in the megakaryocytic cell line Meg-01. The cytokines TPO, interleukin 11 (IL-11), erythropoietin (EPO), and stem cell factor (SCF), which are known stimulators of megakaryopoiesis, but not interleukin3 (IL-3), increased MPLP mRNA detection in PBMC during 96 h of incubation. However, concomitantly the detection of MPLK transcripts decreased in these cells. MPLP was also detected in monocytes, B-lympocyte and T cell populations. In contrast, MPLK mRNA expression was low in monocytes, B and T cells, and no clear increase in transcription detection was observed during stimulation of these cells.

Effects of freeze-dry processing conditions on the crystallization of pentamidine isethionate.

The results of this study show that pentamidine isethionate (PI) can exist in at least four crystalline forms-three anhydrates designated as forms A, B, and C, and a trihydrate. Form C is the high-temperature modification, produced by heating forms A, B, and the trihydrate above 130 degrees C and cannot be produced under actual lyophilization conditions. The crystal forms of PI present after freeze-drying depend on the initial solution concentration and the thermal history of freezing. At low concentrations of PI (4% and less), form A is observed regardless of freezing method. At a higher concentration (10%), the crystal forms observed are a function of the freezing method. Three freezing methods were used to effect different cooling rates: (1) cooling on the shelf to 2 degrees C and holding for 3 h prior to decreasing the temperature to -45 degrees C, (2) directly cooling on the shelf from room temperature to -45 degrees C, and (3) dipping the vials in liquid nitrogen. The results show that form A, form B, or a mixture of both forms are present in the freeze-dried solid depending upon whether the trihydrate crystallizes during freezing or not. Since form B can only be produced by dehydration of the trihydrate at low temperature, the presence of this form in the freeze-dried powders depends on the nucleation and growth of the trihydrate during freezing. Photostability studies have demonstrated marked differences between freeze-dried solids frozen under different conditions. The results underscore the importance of recognizing that seemingly subtle differences in processing conditions can have a significant impact on critical quality attributes of freeze-dried products.

The polymorphic drug substances of the European pharmacopoeia. Part 9. Physicochemical properties and crystal structure of acetazolamide crystal forms.

The crystal structure of acetazolamide modification I (mod. I) was determined, and its differences compared with the already known crystal structure of the triclinic modification II (mod. II) are discussed. The monoclinic mod. I crystallizes in space group P2(1)/n with four molecules in the unit cell: a = 4.7674, b = 21.956, and c = 8.186 A, beta = 104.23 degrees. In both modifications, the molecules form hydrogen-bonded centrosymmetric dimers. The two modifications differ distinctly in the spatial arrangement of these pairs and in the hydrogen bonds formed between them. The thermodynamic relationship between the two modifications is demonstrated by a semischematic energy/temperature diagram, based on the results of thermal analysis and solubility experiments. Mod. II is the thermodynamically stable modification at 20 degrees C and enantiotropically related to mod. I. The thermodynamic transition point lies between 120 and 148 degrees C. The solid-state properties of acetazolamide are mainly directed by the strong intermolecular hydrogen bond forces. Thus, the metastable mod. I exhibits a higher density than mod. II and a very high kinetic stability at 20 degrees C. Both modifications can be crystallized from water and the solubility differences are very small, so, in addition to mod. II, the metastable but extremely resistant mod. I is suggested to be suitable for use in solid pharmaceutical formulations.